Growth of carbon-based nanostructures using active growth materials comprising alkali metals and/or alkaline earth metals

ABSTRACT

The instant disclosure is related to the growth of carbon-based nanostructures and associated systems and products. Certain embodiments are related to carbon-based nanostructure growth using active growth materials comprising alkali metals and/or alkaline earth metals. In some embodiments, the growth of carbon-based nanostructures is performed at relatively low temperatures.

RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofInternational Patent Application No. PCT/US2017/024928, filed Mar. 30,2017, entitled “Growth of Carbon-Based Nanostructures Using ActiveGrowth Materials Comprising Alkali Metals and/or Alkaline Earth Metals”,which claims priority under 35 U.S.C. § 119(e) to U.S. ProvisionalApplication No. 62/315,508, filed Mar. 30, 2016, and entitled “Growth ofCarbon-Based Nanostructures Using Active Growth Materials ComprisingAlkali Metals and/or Alkaline Earth Metals,” each of which isincorporated herein by reference in its entirety for all purposes.

GOVERNMENT SPONSORSHIP

This invention was made with Government support under Grant No.NNX14AL47H awarded by the NASA Goddard Space Flight Center. TheGovernment has certain rights in the invention.

TECHNICAL FIELD

Growth of carbon-based nanostructures and associated systems andproducts are generally described.

BACKGROUND

The production of carbon-based nanostructures may potentially serve asan important tool in the production of a broad array of emergingapplications including electronics and structural materials. Recentresearch has focused on the production of, for example, carbon nanotubes(CNTs) through chemical vapor deposition (CVD) and other techniques. Theselection of an appropriate material on which to form the nanostructuresis important when designing processes for the production of carbonnanostructures. However, many commonly used materials have one or moredisadvantages associated with them.

Accordingly, improved compositions and methods are needed.

SUMMARY

The instant disclosure is related to the growth of carbon-basednanostructures and associated systems and products. Certain embodimentsare related to carbon-based nanostructure growth using active growthmaterials comprising alkali metals and/or alkaline earth metals. In someembodiments, the growth of carbon-based nanostructures is performed atrelatively low temperatures. The subject matter of the present inventioninvolves, in some cases, interrelated products, alternative solutions toa particular problem, and/or a plurality of different uses of one ormore systems and/or articles.

In one aspect, methods of growing carbon-based nanostructures aredescribed. In some embodiments, the method comprises exposing aprecursor of the carbon-based nanostructures to an active growthmaterial comprising at least one of an alkali metal and an alkalineearth metal to grow the carbon-based nanostructures from the precursorof the carbon-based nanostructures.

In certain embodiments, the method comprises exposing a precursor of thecarbon-based nanostructures to an active growth material comprising atleast one of an alkali metal and an alkaline earth metal to grow thecarbon-based nanostructures from the precursor of the carbon-basednanostructures, wherein the active growth material is at a temperatureof less than or equal to 500° C. during the growth of the carbon-basednanostructures; and the active growth material does not contain iron orcontains iron in an amount such that the ratio of the number of atoms ofiron in the active growth material to the combined number of atoms ofany alkali metals and any alkaline earth metals in the active growthmaterial is less than or equal to 3.5.

According to certain embodiments, the method comprises exposing aprecursor of the carbon-based nanostructures to an active growthmaterial comprising at least one of an alkali metal and an alkalineearth metal to grow the carbon-based nanostructures from the precursorof the carbon-based nanostructures, wherein the active growth materialis at a temperature of less than or equal to 475° C. during the growthof the carbon-based nanostructures.

A method of growing carbon-based nanostructures comprises, according tosome embodiments, exposing a precursor of the carbon-basednanostructures to an active growth material comprising at least one ofan alkali metal and an alkaline earth metal to grow the carbon-basednanostructures from the precursor of the carbon-based nanostructures,wherein the precursor of the carbon-based nanostructures comprises bothcarbon dioxide and an alkyne.

Certain aspects are related to inventive articles. In some embodiments,the article comprises a substrate; a polymeric material at leastpartially coating the substrate; carbon-based nanostructures supportedby the substrate; and an active growth material associated with thecarbon-based nanostructures.

In some embodiments, the article comprises a substrate; a plurality ofelongated carbon-based nanostructures supported by the substrate, theelongated carbon-based nanostructures having tortuosities of less thanor equal to 5; and an active growth material associated with thecarbon-based nanostructures.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1A is a cross-sectional schematic illustration showing a method ofgrowing carbon-based nanostructures, according to certain embodiments;

FIG. 1B is, in accordance with some embodiments, a cross-sectionalschematic illustration showing a method of growing carbon-basednanostructures in the absence of a substrate;

FIG. 1C is, according to certain embodiments, a perspective schematicillustration showing a method of growing carbon-based nanostructures onan elongated substrate, such as an unsized or desized carbon fibersubstrate;

FIG. 1D is a perspective schematic illustration showing a method ofgrowing carbon-based nanostructures on an elongated substrate that is atleast partially coated, such as a sized carbon fiber substrate,according to certain embodiments;

FIG. 2 is an exemplary cross-sectional schematic illustration showingpossible interaction volumes between an active growth material and asubstrate;

FIG. 3A is, according to certain embodiments, a cross-sectionalschematic illustration of a highly tortuous nanostructure;

FIG. 3B is a cross-sectional schematic illustration of a moderatelytortuous nanostructure, according to certain embodiments;

FIG. 3C is, in accordance with certain embodiments, a cross-sectionalschematic illustration of a nanostructure having a relatively lowtortuosity;

FIG. 4 is a SEM image of a desized carbon fiber, according to one set ofembodiments;

FIG. 5 is a SEM image of a desized carbon fiber supporting an activegrowth material comprising iron after exposure to carbon-basednanostructure precursors at an elevated temperature, in which nocarbon-based nanostructure growth was observed;

FIGS. 6A-6B are SEM images of desized carbon fibers supporting carbonnanotubes grown from an active growth material comprising sodiumhydroxide, in accordance with certain embodiments;

FIG. 6C is, according to certain embodiments, a TEM image of acarbon-based nanostructure grown from an active growth materialcomprising sodium hydroxide;

FIG. 7 is, in accordance with certain embodiments, an SEM image of sizedcarbon fibers supporting carbon nanotubes grown from an active growthmaterial comprising sodium hydroxide;

FIG. 8 is an SEM image of sized carbon fibers supporting carbonnanotubes grown from an active growth material comprising sodiumcarbonate, according to some embodiments;

FIG. 9 is an SEM image of sized carbon fibers supporting carbonnanotubes grown from an active growth material comprising sodiumbicarbonate, according to certain embodiments;

FIG. 10 is, in accordance with some embodiments, an SEM image of aluminafibers supporting carbon nanotubes grown from an active growth materialcomprising sodium hydroxide;

FIGS. 11A-11F are SEM images of poly(styrene-alt-maleic acid)-coatedglass slides supporting carbon nanotubes grown from an active growthmaterial comprising sodium hydroxide, according to certain embodiments;

FIGS. 12A-12F are SEM images of poly(styrene-alt-maleic acid)-coatedglass slides supporting carbon nanotubes grown from an active growthmaterial comprising potassium carbonate, in accordance with someembodiments;

FIGS. 13A-13E are, according to some embodiments, SEM images of titaniumsupporting carbon nanotubes grown from an active growth materialcomprising sodium carbonate;

FIGS. 14A-14F are, in accordance with some embodiments, SEM images oftitanium supporting carbon nanotubes grown from an active growthmaterial comprising sodium bicarbonate;

FIGS. 15A-15F are SEM images of titanium supporting carbon nanotubesgrown from an active growth material comprising sodium hydroxide,according to some embodiments;

FIGS. 16A-16D are SEM images of titanium supporting carbon nanotubesgrown from an active growth material comprising sodium hydroxide, inaccordance with certain embodiments;

FIG. 17 is a composite panel of four micrographs showing carbonnanostructure growth from a variety of active growth materials,according to some embodiments;

FIG. 18 is a composite panel of four micrographs showing carbonnanostructure growth on a variety of substrates, according to someembodiments;

FIG. 19 is a composite panel of six micrographs showing carbonnanostructure growth at a variety of temperatures, according to someembodiments;

FIG. 20 is a composite panel of six micrographs showing carbonnanostructure growth at a variety of CO₂ and C₂H₂ concentrations,according to some embodiments;

FIG. 21 is a composite panel of eight micrographs showing carbonnanostructure growth after a variety of times, according to someembodiments; and

FIG. 22 is a composite panel of four micrographs showing carbonnanostructures.

DETAILED DESCRIPTION

Systems and methods for the growth of carbon-based nanostructures aregenerally described. In some embodiments, the nanostructures may begrown on an active growth material. The active growth material, or aprecursor thereof, can comprise, in some embodiments, at least one of analkali metal and an alkaline earth metal. That is to say, all or part ofthe active growth material, or a precursor thereof, may be made up ofone or more alkali metals and/or one or more alkaline earth metals,according to certain embodiments. The carbon-based nanostructures may begrown by exposing a precursor of the carbon-based nanostructures to theactive growth material, in the presence or absence of a growthsubstrate, such that the carbon-based nanostructures are grown from theprecursor. This may be achieved, for example, by exposing the precursorand the active growth material to a set of conditions that causes growth(e.g., nucleation and/or additional growth) of carbon-basednanostructures on the active growth material. In some such embodiments,one or more of the conditions can be selected to form carbon-basednanostructures from the precursor on the active growth material.

The growth of the carbon-based nanostructures may be achieved atrelatively low temperatures, according to certain embodiments. Forexample, in some embodiments, the precursor of the carbon-basednanostructures (and/or the active growth material, and/or the optionalgrowth substrate) may be at a temperature of less than or equal to 500°C. (or less than or equal to 475° C., or lower) during the growth of thecarbon-based nanostructures. Other temperatures and temperature rangesare also possible, and are discussed further below.

According to certain embodiments, the alkaline earth metals and/or thealkali metals may make up a relatively large percentage of the activegrowth material, or a precursor thereof, relative to, for example, ironor other traditional catalyst materials such as other transition metals.For example, in some cases, the ratio of the number of atoms of iron inthe active growth material, or a precursor thereof, to the combinednumber of atoms of any alkali metals and any alkaline earth metals inthe active growth material, or a precursor thereof, is less than orequal to 3.5. In some embodiments, the ratio of the combined number ofatoms of all transition metals in the active growth material, or aprecursor thereof, to the combined number of atoms of any alkali metalsand any alkaline earth metals in the active growth material, or aprecursor thereof, is less than or equal to 3.5.

Without wishing to be bound by any particular theory, it is believedthat the use of alkali metals and/or alkaline earth metals in the activegrowth material can, according to certain although not necessarily allembodiments, allow for the growth of carbon-based nanostructures atrelatively low temperatures. The ability to grow carbon-basednanostructures at relatively low temperatures can be advantageous as itmay, according to certain although not necessarily all embodiments,reduce the amount of energy required to grow the carbon-basednanostructures and/or allow for the growth of carbon-basednanostructures on temperature sensitive substrates (e.g., polymers andother temperature sensitive substrates), as described in more detailbelow.

As described in more detail below, certain of the systems and methodsdescribed herein may be used to grow a variety of carbon-basednanostructures, including carbon nanotubes, carbon nanofibers, andcarbon nanowires. Certain embodiments described herein may beparticularly useful, in certain cases, for growing carbon nanotubes.

As noted above, certain embodiments are related to methods of growingcarbon-based nanostructures. According to some embodiments, the methodof growing carbon-based nanostructures comprises providing an activegrowth material or an active growth material precursor and exposing aprecursor of the carbon-based nanostructures to the active growthmaterial or active growth material precursor comprising at least one ofan alkali metal and an alkaline earth metal to grow the carbon-basednanostructures from the precursor. It should be understood that, whereactive growth materials and their associated properties are describedbelow and elsewhere herein, either or both of the active growth materialitself and the active growth material precursor may have the propertiesdescribed as being associated with the active growth material. In someembodiments, the active growth material and/or the active growthmaterial precursor has these properties upon being exposed to thecarbon-based nanostructure precursor. In certain embodiments, the activegrowth material and/or the active growth material precursor has theseproperties at the beginning of a heating step used to form thecarbon-based nanostructures. In certain embodiments, the active growthmaterial and/or the active growth material precursor has theseproperties at at least one point in time during which the material is ina chamber or other vessel within which the carbon-based nanostructuresare grown.

An exemplary system 100 for growing carbon-based nanostructures is shownin FIG. 1A. In FIG. 1A, carbon-based nanostructures 102 are grown byexposing active growth material 106 to precursor 104 of carbon-basednanostructures 102. As illustrated in FIG. 1A, active growth material106 is in contact (e.g., direct contact) with optional growth substrate108, but in other embodiments, the active growth material is not incontact with a growth substrate. For example, in FIG. 1B, active growthmaterial 106 is not in contact with an underlying substrate. In someembodiments, the active growth material may be in contact with thesubstrate prior to a growth process, but may be displaced from thesubstrate during a growth process by a growing carbon-basednanostructure.

Active growth material 106 (e.g., a nanoparticle of active growthmaterial) can comprise one or more alkali metals and/or one or morealkaline earth metals. Specific examples of active growth materials aredescribed in more detail below. According to certain embodiments, theactive growth material catalyzes the growth of the carbon-basednanostructures.

It should be understood that the growth of carbon-based nanostructurescan include the initial nucleation/formation of the carbon-basednanostructure and/or making an existing carbon-based nanostructurelarger in size. In certain embodiments, the growth of the carbon-basednanostructures comprises nucleating or otherwise forming thecarbon-based nanostructures from material that is not a carbon-basednanostructure.

In some embodiments, two or more carbon-based nanostructures maynucleate or otherwise form from a material that is not a carbon-basednanostructure. The two or more carbon-based nanostructures may be thesame type of carbon-based nanostructure, or may be different types ofcarbon-based nanostructures. In some embodiments, the growth of thecarbon-based nanostructures comprises making an existing carbon-basednanostructure larger in size. The growth process can also include bothof these steps, in some cases. In certain embodiments, multiple growthsteps can be performed, for example, using a single active growthmaterial to grow carbon-based nanostructures multiple times.

The precursor of the carbon-based nanostructures can be exposed to theactive growth material in a number of ways. Generally, exposing theactive growth material to the precursor comprises combining theprecursor and the active growth material with each other such that theyare in contact. According to certain embodiments, exposing the precursorof the carbon-based nanostructures to the active growth materialcomprises adding the precursor of the carbon-based nanostructures to theactive growth material. In certain embodiments, exposing the precursorof the carbon-based nanostructures to the active growth materialcomprises adding the active growth material to the precursor of thecarbon-based nanostructures. In still other embodiments, the precursorof the carbon-based nanostructures and the active growth material can bemixed simultaneously. Other methods of exposure are also possible.Exposing the precursor of the carbon-based nanostructures to an activegrowth material can occur, according to some embodiments, in a chamberor other volume. The volume in which the precursor of the carbon-basednanostructures is exposed to the active growth material may be fullyenclosed, partially enclosed, or completely unenclosed.

As noted above, according to certain embodiments, the precursor of thecarbon-based nanostructures can be exposed to the active growth materialto grow the carbon-based nanostructures from the precursor. For example,in FIG. 1A, nanostructure precursor material 104, may be delivered tooptional substrate 108 and contact or permeate the substrate surface(e.g., via arrow 112), the active growth material surface (e.g., viaarrow 114), and/or the interface between the active growth material andthe substrate (e.g., via arrow 110).

According to certain embodiments, carbon from the precursor of thecarbon-based nanostructures may be dissociated from the precursor. Thedissociation of the carbon from the precursor can, according to certainembodiments, involve the breaking of at least one covalent bond. Inother cases, the dissociation of the carbon from the precursor does notinvolve breaking a covalent bond. The carbon dissociated from theprecursor may, according to certain embodiments, chemically react togrow the carbon-based nanostructures via the formation of new covalentbonds (e.g., new carbon-carbon covalent bonds). In the growth of carbonnanotubes, for example, the nanostructure precursor material maycomprise carbon, such that carbon dissociates from the precursormolecule and may be incorporated into the growing carbon nanotube viathe formation of new carbon-carbon covalent bonds. Referring to FIG. 1A,according to certain embodiments, nanostructure precursor 104 maycomprise carbon, such that carbon dissociates from nanostructureprecursor 104 (optionally, breaking a covalent bond) and is incorporatedinto growing carbon-based nanostructures 102. The growing carbon-basednanostructures may, for example, extend upward from the growth substratein general direction 116 with continued growth.

As described in more detail below, a variety of materials can be used asthe precursor of the carbon-based nanostructures and as the activegrowth material (or a precursor of the active growth material).According to certain embodiments, carbon-based nanostructures (e.g.,carbon nanotubes) may be synthesized using CO₂ and acetylene asprecursors of the carbon-based nanostructures. In some such embodiments,the active growth material, or a precursor thereof, comprisesnanoparticles of sodium hydroxide salts, which optionally may bearranged on a carbon fiber support (e.g., a sized, unsized, or desizedcarbon fiber support). Other examples of nanostructure precursormaterials, active growth materials, precursors of active growthmaterials, and the types of carbon-based nanostructures that may begrown using these materials are described in more detail below.

In some embodiments, the method of growing carbon-based nanostructurescomprises exposing the active growth material and the precursor of thecarbon-based nanostructures to a set of conditions that causes growth ofcarbon-based nanostructures on the active growth material. Growth of thecarbon-based nanostructures may comprise, for example, heating theprecursor of the carbon-based nanostructures, the active growthmaterial, or both. Other examples of suitable conditions under which thecarbon-based nanostructures may be grown are described in more detailbelow. In some embodiments, growing carbon-based nanostructurescomprises performing chemical vapor deposition (CVD) of nanostructureson the active growth material. In some embodiments, the chemical vapordeposition process may comprise a plasma chemical vapor depositionprocess. Chemical vapor deposition is a process known to those ofordinary skill in the art, and is explained, for example, in DresselhausM S, Dresselhaus G., and Avouris, P. eds. “Carbon Nanotubes: Synthesis,Structure, Properties, and Applications” (2001) Springer, which isincorporated herein by reference in its entirety. Examples of suitablenanostructure fabrication techniques are discussed in more detail inInternational Patent Application Serial No. PCT/US2007/011914, filed May18, 2007, entitled “Continuous Process for the Production ofNanostructures Including Nanotubes,” published as WO 2007/136755 on Nov.29, 2007, which is incorporated herein by reference in its entirety.

As noted above, according to certain embodiments, carbon-basednanostructures can be grown by exposing the nanostructure precursor toan active growth material. As used herein, the term “active growthmaterial” refers to a material that, when exposed to a set of conditionsselected to cause growth of nanostructures, either enables growth ofnanostructures that would otherwise not occur in the absence of theactive growth material under essentially identical conditions, orincreases the rate of growth of nanostructures relative to the rate thatwould be observed under essentially identical conditions but without theactive growth material. “Essentially identical conditions,” in thiscontext, means conditions that are similar or identical (e.g., pressure,temperature, composition and concentration of species in theenvironment, etc.), other than the presence of the active growthmaterial. In some embodiments, the active growth material can be part ofa larger material (e.g., when the active growth material corresponds toa doped portion of a structure doped with an active material such as analkali or alkaline earth metal the like). In other cases, the activegrowth material can be a single, standalone structure (e.g., when theactive growth material is a particle made up of one or more alkali metaland/or one or more alkaline earth metal, etc.). In certain embodiments,the active growth material is active throughout its exposed surface. Insome embodiments, the active growth material is active throughout atleast some or all of its volume.

In accordance with certain embodiments, the active growth material isnot incorporated into the carbon-based nanostructures during growth. Forexample, the active growth material, according to certain embodiments,is not covalently bonded to the carbon-based nanostructure grown fromthe precursor. In some embodiments, the active growth material isincorporated into the carbon-based nanostructure during growth. Forexample, growth may result in the formation of a material that comprisesa carbon-based nanostructure surrounding the active growth material(e.g., a carbon nanotube where at least a portion of the active growthmaterial is disposed inside the carbon nanotube, a carbon nanotube whereat least a portion of the active growth material lines an inner wall ofa carbon nanotube).

In some embodiments, the active growth material lowers the activationenergy of the chemical reaction used to grow the carbon-basednanostructures from the precursor. According to certain embodiments, theactive growth material catalyzes the chemical reaction(s) by which thecarbon-based nanostructures are grown from the precursor.

In certain embodiments, the active growth material is formed from anactive growth material precursor which undergoes a phase change orchemical change prior to carbon-based nanostructure growth. As notedabove, it should be understood that, where active growth materials andtheir associated properties are described elsewhere herein, either orboth of the active growth material itself and the active growth materialprecursor may have the properties described as being associated with theactive growth material. In some embodiments, an active growth materialprecursor may be provided (e.g., applied to an optional substrate) inone form and then undergo a physical or chemical transition (e.g.,during a heating step, during exposure to a nanostructure precursor)prior to forming the active growth material. For example, in someembodiments, the active growth material precursor may melt, becomeoxidized or reduced, become activated, or undergo any physical orchemical change prior to forming the active growth material. Generally,in embodiments in which the active growth material is formed from aprecursor, the alkaline earth metal and/or alkali metal of the activegrowth material corresponds to the alkaline earth metal and/or alkalimetal of the active growth material precursor from which it is formed.Of course, according to certain embodiments, the active growth materialitself may have any of the properties described herein with respect toactive growth materials and their precursors.

As noted above, in some embodiments, the active growth material, or aprecursor thereof, comprises at least one of an alkali metal and analkaline earth metal. In some embodiments, the active growth material,or a precursor thereof, comprises an alkali metal. For example, theactive growth material, or a precursor thereof, can comprise a singlealkali metal or a combination of multiple alkali metals. According tosome embodiments, the active growth material, or a precursor thereof,comprises an alkaline earth metal. For example, the active growthmaterial, or a precursor thereof, can comprise a single alkaline earthmetal or a combination of multiple alkaline earth metals. In certainembodiments, the active growth material, or a precursor thereof,comprise both an alkaline earth metal (e.g., one or more alkaline earthmetals) and an alkali earth metal (e.g., one or more alkaline earthmetals).

The term “alkali metal” is used herein to refer to the following sixchemical elements of Group 1 of the periodic table: lithium, sodium,potassium, rubidium, cesium, and francium. Elemental alkali metals areuncharged but are capable of becoming oxidized to form ions with a +1oxidation state. In accordance with some embodiments, the active growthmaterial, or a precursor thereof, may comprise one or more alkali metalsin any oxidation state or any combination of oxidation states. Incertain embodiments, the alkali metal in the active growth material, ora precursor thereof, is the cation of a salt. In certain embodiments,the alkali metal or the precursor thereof is not in the form of anoxide. In some embodiments, the alkali metal or the precursor thereof isnot in the form of a chalcogenide. In certain embodiments, the alkalimetal or the precursor thereof is not in the form of a carbide. In someembodiments, the alkali metal in the active growth material, or aprecursor thereof, is a component of an alloy. In certain embodiments,the alkali metal in the active growth material, or a precursor thereof,is in its elemental form. Other components of active growth materials,or precursors thereof, which contain alkali metals may be one or more ofatoms in any oxidation state, polyatomic ions with any charge, andmolecules with any molecular weight and charge, in accordance with someembodiments. In certain embodiments, the alkali metal and/or othercomponents of the active growth material, or a precursor thereof, may bein the same oxidation state throughout the processes of active growthmaterial deposition and nanostructure growth. In other embodiments, thealkali metal and/or other components of the active growth material maytransition from one oxidation state to another oxidation state duringthe processes of active growth material deposition and/or nanostructuregrowth. In accordance with some embodiments, the alkali metal and/orother components of the active growth material may be in the sameoxidation state after nanostructure growth has been completed as beforeand/or during nanostructure growth. In accordance with otherembodiments, the alkali metal and/or other components of the activegrowth material may be in a different oxidation state afternanostructure growth has been completed as before and/or duringnanostructure growth. The term “alkaline earth metal” is used herein torefer to the six chemical elements in Group 2 of the periodic table:beryllium, magnesium, calcium, strontium, barium, and radium. Elementalalkaline earth metals are uncharged but are capable of becoming oxidizedto form ions with a +1 or +2 oxidation state. In accordance with someembodiments, the active growth material, or a precursor thereof, maycomprise one or more alkaline earth metals in any oxidation state or anycombination of oxidation states. In certain embodiments, the alkalineearth metal in the active growth material, or a precursor thereof, isthe cation of a salt. In certain embodiments, the alkaline earth metalor the precursor thereof is not in the form of an oxide. In someembodiments, the alkaline earth metal or the precursor thereof is not inthe form of a chalcogenide. In certain embodiments, the alkaline earthmetal or the precursor thereof is not in the form of a carbide. In someembodiments, the alkaline earth metal in the active growth material, ora precursor thereof, is a component of an alloy. In certain embodiments,the alkaline earth metal in the active growth material, or a precursorthereof, is in its elemental form. Combinations of these are alsopossible. Other components of active growth materials, or precursorsthereof, which contain alkaline earth metals may be one or more of atomsin any oxidation state, polyatomic ions with any charge, and moleculeswith any molecular weight and charge, in accordance with someembodiments. In certain embodiments, the alkaline earth metal and/orother components of the active growth material, or a precursor thereof,may be in the same oxidation state throughout the processes of activegrowth material deposition and nanostructure growth. In otherembodiments, the alkaline earth metal and/or other components of theactive growth material may transition from one oxidation state toanother oxidation state during the processes of active growth materialdeposition and/or nanostructure growth. In accordance with someembodiments, the alkaline earth metal and/or other components of theactive growth material may be in the same oxidation state afternanostructure growth has been completed as before and/or duringnanostructure growth. In accordance with other embodiments, the alkalineearth metal and/or other components of the active growth material may bein a different oxidation state after nanostructure growth has beencompleted as before and/or during nanostructure growth.

In certain embodiments, the active growth material, or a precursorthereof, comprises at least one of sodium and potassium. In some suchembodiments, the active growth material, or a precursor thereof,contains only sodium and no potassium. In other embodiments, the activegrowth material, or a precursor thereof, contains only potassium and nosodium. In other embodiments, the active growth material, or a precursorthereof, contains both sodium and potassium.

In certain embodiments, the active growth material, or a precursorthereof, comprises at least one of a hydroxide salt of an alkaline earthmetal and a hydroxide salt of an alkali metal. In some embodiments, theactive growth material, or a precursor thereof, comprises a hydroxidesalt of an alkaline earth metal but does not comprise a hydroxide saltof an alkali metal. In certain embodiments, the active growth material,or a precursor thereof, comprises a hydroxide salt of an alkali metalbut does not comprise a hydroxide salt of an alkaline earth metal. Inother embodiments, the active growth material, or a precursor thereof,comprises both a hydroxide salt of an alkaline earth metal and ahydroxide salt of an alkali metal.

A hydroxide salt is a salt comprising OH⁻ ions. In some embodiments, thehydroxide salt may contain only OH⁻ anions; in other embodiments, thehydroxide salt may additionally contain other anions. The additionalanions in such a salt may have any negative oxidation state, may bemonatomic or polyatomic, may have any molecular weight, and may beorganic ions or inorganic ions. In accordance with certain embodiments,the hydroxide salt may additionally comprise cations which are neitheralkali metals nor alkaline earth metals. These cations may have anypositive oxidation state, may be monatomic or polyatomic, may have anymolecular weight, and may be organic ions or inorganic ions. The ratioof OH⁻ anions to the alkaline earth metal(s) and/or alkali metal(s) inthe hydroxide salt generally depends upon the oxidation states of thesemetals, the oxidation states of the other cations and/or anions withinthe salt, and the overall ratios of each of the other ions to eachother. The hydroxide salt may further comprise bound water in someembodiments. In other embodiments, the hydroxide salt may be water free.

According to certain embodiments, the OH⁻ ions make up at least acertain percentage of the total number of anions within the hydroxidesalt. In some embodiments, the OH⁻ ions make up at least 50%, at least75%, at least 90%, at least 95%, or at least 99% of the total number ofanions within the hydroxide salt. In certain embodiments, the OH⁻ ionsmake up less than or equal to 100%, less than 99%, less than 95%, lessthan 90%, or less than 75% of the total number of anions within thehydroxide salt. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 95% and less than or equal to100% of the total number of anions within the hydroxide salt). Otherranges are also possible.

In certain embodiments, the active growth material, or a precursorthereof, comprises at least one of a carbonate salt of an alkaline earthmetal and a carbonate salt of an alkali metal. In some embodiments, theactive growth material, or a precursor thereof, comprises a carbonatesalt of an alkaline earth metal but does not comprise a carbonate saltof an alkali metal. In certain embodiments, the active growth material,or a precursor thereof, comprises a carbonate salt of an alkali metalbut does not comprise a carbonate salt of an alkaline earth metal. Inother embodiments, the active growth material, or a precursor thereof,comprises both a carbonate salt of an alkaline earth metal and acarbonate salt of an alkali metal.

A carbonate salt is a salt comprising CO₃ ²⁻ ions. In some embodiments,the carbonate salt may contain only CO₃ ²⁻ anions; in other embodiments,the carbonate salt may additionally contain other anions. The additionalanions in such a salt may have any negative oxidation state, may bemonatomic or polyatomic, may have any molecular weight, and may beorganic ions or inorganic ions. In accordance with certain embodiments,the carbonate salt may additionally comprise cations which are neitheralkali metals nor alkaline earth metals. These cations may have anypositive oxidation state, may be monatomic or polyatomic, may have anymolecular weight, and may be organic ions or inorganic ions. The ratioof CO₃ ²⁻ anions to the alkaline earth metal(s) and/or alkali metal(s)in the carbonate salt generally depends upon the oxidation states ofthese metals, the oxidation states of the other cations and/or anionswithin the salt, and the overall ratios of each of the other ions toeach other. The amount of CO₃ ²⁻ anions in the carbonate salt willgenerally be determined by the total mass of the carbonate salt and willbe such that the salt has a net zero total charge. The carbonate saltmay further comprise bound water in some embodiments. In otherembodiments, the carbonate salt may be water free.

According to certain embodiments, the CO₃ ²⁻ ions make up at least acertain percentage of the total number of anions within the carbonatesalt. In some embodiments, the CO₃ ²⁻ ions make up at least 50%, atleast 75%, at least 90%, at least 95%, or at least 99% of the totalnumber of anions within the carbonate salt. In certain embodiments, theCO₃ ²⁻ ions make up less than or equal to 100%, less than 99%, less than95%, less than 90%, or less than 75% of the total number of anionswithin the carbonate salt. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 95% and less than orequal to 100% of the total number of anions within the bicarbonatesalt). Other ranges are also possible.

In certain embodiments, the active growth material, or a precursorthereof, comprises at least one of a bicarbonate salt of an alkalineearth metal and a bicarbonate salt of an alkali metal. In someembodiments, the active growth material, or a precursor thereof,comprises a bicarbonate salt of an alkaline earth metal but does notcomprise a bicarbonate salt of an alkali metal. In certain embodiments,the active growth material, or a precursor thereof, comprises abicarbonate salt of an alkali metal but does not comprise a bicarbonatesalt of an alkaline earth metal. In other embodiments, the active growthmaterial, or a precursor thereof, comprises both a bicarbonate salt ofan alkaline earth metal and a bicarbonate salt of an alkali metal.

A bicarbonate salt is a salt comprising HCO₃ ⁻ ions. In someembodiments, the bicarbonate salt may contain only HCO₃ ⁻ anions; inother embodiments, the bicarbonate salt may additionally contain otheranions. The additional anions in such a salt may have any negativeoxidation state, may be monatomic or polyatomic, may have any molecularweight, and may be organic ions or inorganic ions. In accordance withcertain embodiments, the bicarbonate salt may additionally comprisecations which are neither alkali metals nor alkaline earth metals. Thesecations may have any positive oxidation state, may be monatomic orpolyatomic, may have any molecular weight, and may be organic ions orinorganic ions. The ratio of HCO₃ ⁻ anions to the alkaline earthmetal(s) and/or alkali metal(s) in the bicarbonate salt generallydepends upon the oxidation states of these metals, the oxidation statesof the other cations and/or anions within the salt, and the overallratios of each of the other ions to each other. The amount of HCO₃ ⁻anions in the bicarbonate salt will generally be determined by the totalmass of the bicarbonate salt and will be such that the salt has a netzero total charge. The bicarbonate salt may further comprise bound waterin some embodiments. In other embodiments, the bicarbonate salt may bewater free.

According to certain embodiments, the HCO₃ ⁻ ions make up at least acertain percentage of the total number of anions within the bicarbonatesalt. In some embodiments, the HCO₃ ⁻ ions make up at least 50%, atleast 75%, at least 90%, at least 95%, or at least 99% of the totalnumber of anions within the bicarbonate salt. In certain embodiments,the HCO₃ ⁻ ions make up less than or equal to 100%, less than 99%, lessthan 95%, less than 90%, or less than 75% of the total number of anionswithin the bicarbonate salt. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 95% and less than orequal to 100% of the total number of anions within the bicarbonatesalt). Other ranges are also possible.

In certain embodiments, the active growth material, or a precursorthereof, comprises at least one of a halide salt of an alkaline earthmetal and a halide salt of an alkali metal. In some embodiments, theactive growth material, or a precursor thereof, comprises a halide saltof an alkaline earth metal but does not comprise a halide salt of analkali metal. In certain embodiments, the active growth material, or aprecursor thereof, comprises a halide salt of an alkali metal but doesnot comprise a halide salt of an alkaline earth metal. In otherembodiments, the active growth material, or a precursor thereof,comprises both a halide salt of an alkaline earth metal and a halidesalt of an alkali metal.

A halide salt is a salt comprising halide ions. The term “halide ion” isused herein to refer to negatively charged ions of following fivechemical elements of Group 1 of the periodic table: fluorine, chlorine,bromine, iodine, and astatine. In some embodiments, the halide salt maycontain only halide anions; in other embodiments, the halide salt mayadditionally contain other anions. The additional anions in such a saltmay have any negative oxidation state, may be monatomic or polyatomic,may have any molecular weight, and may be organic ions or inorganicions. In accordance with certain embodiments, the halide salt mayadditionally comprise cations which are neither alkali metals noralkaline earth metals. These cations may have any positive oxidationstate, may be monatomic or polyatomic, may have any molecular weight,and may be organic ions or inorganic ions. The ratio of halide anions tothe alkaline earth metal(s) and/or alkali metal(s) in the halide saltgenerally depends upon the oxidation states of these metals, theoxidation states of the other cations and/or anions within the salt, andthe overall ratios of each of the other ions to each other. The halidesalt may further comprise bound water in some embodiments. In otherembodiments, the halide salt may be water free.

According to certain embodiments, the halide ions make up at least acertain percentage of the total number of anions within the halide salt.In some embodiments, the halide ions make up at least 50%, at least 75%,at least 90%, at least 95%, or at least 99% of the total number ofanions within the halide salt. In certain embodiments, the halide ionsmake up less than or equal to 100%, less than 99%, less than 95%, lessthan 90%, or less than 75% of the total number of anions within thehalide salt. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 95% and less than or equal to100% of the total number of anions within the halide salt). Other rangesare also possible.

In certain embodiments, the active growth material, or a precursorthereof, comprises at least one of a chloride salt of an alkaline earthmetal and a chloride salt of an alkali metal. In some embodiments, theactive growth material, or a precursor thereof, comprises a chloridesalt of an alkaline earth metal but does not comprise a chloride salt ofan alkali metal. In certain embodiments, the active growth material, ora precursor thereof, comprises a chloride salt of an alkali metal butdoes not comprise a chloride salt of an alkaline earth metal. In otherembodiments, the active growth material, or a precursor thereof,comprises both a chloride salt of an alkaline earth metal and a chloridesalt of an alkali metal.

A chloride salt is a salt comprising chloride ions. In some embodiments,the chloride salt may contain only chloride anions; in otherembodiments, the chloride salt may additionally contain other anions.The additional anions in such a salt may have any negative oxidationstate, may be monatomic or polyatomic, may have any molecular weight,and may be organic ions or inorganic ions. In accordance with certainembodiments, the chloride salt may additionally comprise cations whichare neither alkali metals nor alkaline earth metals. These cations mayhave any positive oxidation state, may be monatomic or polyatomic, mayhave any molecular weight, and may be organic ions or inorganic ions.The ratio of chloride anions to the alkaline earth metal(s) and/oralkali metal(s) in the chloride salt generally depends upon theoxidation states of these metals, the oxidation states of the othercations and/or anions within the salt, and the overall ratios of each ofthe other ions to each other. The chloride salt may further comprisebound water in some embodiments. In other embodiments, the chloride saltmay be water free.

According to certain embodiments, the chloride ions make up at least acertain percentage of the total number of anions within the chloridesalt. In some embodiments, the chloride ions make up at least 50%, atleast 75%, at least 90%, at least 95%, or at least 99% of the totalnumber of anions within the chloride salt. In certain embodiments, thechloride ions make up less than or equal to 100%, less than 99%, lessthan 95%, less than 90%, or less than 75% of the total number of anionswithin the chloride salt. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 95% and less than orequal to 100% of the total number of anions within the chloride salt).Other ranges are also possible.

In certain embodiments, the alkali metal and/or the alkali earth metalis a cation of a salt ionically bound to an anion having a molecularweight of less than or equal to 1000 Daltons. In a salt, ions aretypically bound to numerous other ions throughout the material.

In some embodiments the percentage of the total anions having amolecular weight less than or equal to 1000 Da may be less than or equalto 10%, less than or equal to 5%, less than or equal to 2%, or less thanor equal to 1%. The percentage of the total anions having a molecularweight of less than or equal to 1000 Da may be identically 0%. Thepercentage of the total anions having a molecular weight less than orequal to 1000 Da may be greater than or equal to 0%, greater than orequal to 2%, or greater than or equal to 5%. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0% and less than or equal to 2%). Other ranges are also possible.

In accordance with certain embodiments, the number average molecularweight of the anions is less than or equal to 1000 Da, less than orequal to 750 Da, less than or equal to 500 Da, less than or equal to 250Da, less than or equal to 100 Da, less than or equal to 50 Da, or lessthan or equal to 25 Da. The number average molecular weight of theanions may be greater than or equal to 10 Da, greater than or equal to25 Da, greater than or equal to 50 Da, greater than or equal to 100 Da,greater than or equal to 250 Da, greater than or equal to 500 Da, orgreater than or equal to 750 Da. Combinations of the above-referencedranges are also possible (for example, greater than or equal to 50 Daand less than or equal to 250 Da). Other ranges are also possible.

In accordance with certain embodiments, the weight average molecularweight of the anions is less than or equal to 1000 Da, less than orequal to 750 Da, less than or equal to 500 Da, less than or equal to 250Da, less than or equal to 100 Da, less than or equal to 50 Da, or lessthan or equal to 25 Da. The weight average molecular weight of theanions may be greater than or equal to 10 Da, greater than or equal to25 Da, greater than or equal to 50 Da, greater than or equal to 100 Da,greater than or equal to 250 Da, greater than or equal to 500 Da, orgreater than or equal to 750 Da. Combinations of the above-referencedranges are also possible (for example, greater than or equal to 50 Daand less than or equal to 250 Da). Other ranges are also possible.

One of ordinary skill in the art will be able to determine numberaverage molecular weights and weight average molecular weights using,for example, mass spectroscopy, nuclear magnetic resonance, and/or gelpermeation chromatography (GPC).

The anions may have any chemical structure and any negative oxidationstate, in accordance with certain embodiments. In some embodiments, oneor more anions may be monatomic or polyatomic. The anions may be organicor inorganic, in some embodiments. Each anion may have the same chemicalformula or different anions may have different coordination numbers, inaccordance with certain embodiments. According to certain embodiments,the anions may have coordination numbers ranging from 4 to 12. Eachanion may have the same coordination number or the anions may compriseions of differing coordination numbers.

Non-limiting examples of compounds that may be used as active growthmaterials (or active growth material precursors) include, but are notlimited to, calcium carbonate, sodium carbonate, sodium bicarbonate,sodium hydroxide, potassium carbonate, potassium bicarbonate, andpotassium hydroxide. Additional examples of compounds that could be usedin the active growth material include, but are not limited to, alloyscomprising alkali metals and/or alkaline earth metals, such assodium-potassium alloys (e.g., NaK), cobalt-sodium alloys (e.g., CoNa),and iron-potassium alloys (e.g., FeK).

In some embodiments, the active growth material, or a precursor thereof,contains a relatively low amount of iron. For example, in someembodiments, the active growth material, or a precursor thereof, doesnot contain iron or contains iron in an amount such that the ratio ofthe number of atoms of iron in the active growth material, or aprecursor thereof, to the combined number of atoms of any alkali metalsand any alkaline earth metals in the active growth material, or aprecursor thereof, is less than or equal to 3.5. In certain embodiments,the active growth material, or a precursor thereof, contains iron in anamount such that the ratio of the number of atoms of iron in the activegrowth material, or a precursor thereof, to the combined number of atomsof any alkali metals and alkaline earth metals in the active growthmaterial, or a precursor thereof, is less than or equal to 3.5, lessthan or equal to 3, less than or equal to 2.5, less than or equal to 2,less than or equal to 1, less than or equal to 0.2, less than or equalto 0.1, less than or equal to 0.05, or less than or equal to 0.01. Insome embodiments, the active growth material, or a precursor thereof,contains iron in an amount such that the ratio of the number of atoms ofiron in the active growth material, or a precursor thereof, to thecombined number of atoms of any alkali metals and alkaline earth metalsin the active growth material, or a precursor thereof, is identically 0.Other ranges are also possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the combined number of atoms of any alkalimetals and alkaline earth metals in the active growth material, or aprecursor thereof, can be calculated in the following manner. First, thetotal number of alkali metal atoms in the active growth material, or aprecursor thereof, is determined. Then, the total number of alkalineearth metal atoms in the active growth material, or a precursor thereof,is determined. After this step, the total number of iron atoms in theactive growth material, or a precursor thereof, is determined. Finally,the following formula is used to determine the ratio of the number ofatoms of iron in the active growth material, or a precursor thereof, tothe combined number of atoms of any alkali metals and alkaline earthmetals in the active growth material, or a precursor thereof:

${r_{{iron}:{{alkali}\mspace{14mu} {and}\mspace{14mu} {alkaline}}} = \frac{n_{{total}\mspace{14mu} {iron}}}{n_{{total}\mspace{14mu} {al}\; {kaline}\mspace{14mu} {earth}} + n_{{total}\mspace{14mu} {alkali}}}},$

where r_(iron:alkali and alkaline) is the ratio of the number of atomsof iron in the active growth material, or a precursor thereof, to thecombined number of atoms of any alkali metals and alkaline earth metalsin the active growth material, or a precursor thereof;n_(total alkaline earth) is the total number of alkaline earth metalatoms in the active growth material, or a precursor thereof;n_(total alkali) is the total number of alkali metal atoms in the activegrowth material, or a precursor thereof; and n_(total iron) is the totalnumber of iron atoms in the active growth material, or a precursorthereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain iron or contains iron in an amount such that the ratioof the number of atoms of iron in the active growth material, or aprecursor thereof, to the number of atoms of any alkali metals in theactive growth material, or a precursor thereof, is less than or equal to3.5. In certain embodiments, the active growth material, or a precursorthereof, contains iron in an amount such that the ratio of the number ofatoms of iron in the active growth material, or a precursor thereof, tothe number of atoms of any alkali metals is less than or equal to 3.5,less than or equal to 3, less than or equal to 2.5, less than or equalto 2, less than or equal to 1, less than or equal to 0.2, less than orequal to 0.1, less than or equal to 0.05, or less than or equal to 0.01.In some embodiments, the active growth material, or a precursor thereof,contains iron in an amount such that the ratio of the number of atoms ofiron in the active growth material, or a precursor thereof, to thenumber of atoms of any alkali metals is identically 0. Other ranges arealso possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the number of atoms of any alkali metals inthe active growth material, or a precursor thereof, can be calculated inthe following manner. First, the total number of alkali metal atoms inthe active growth material, or a precursor thereof, is determined. Afterthis step, the total number of iron atoms in the active growth material,or a precursor thereof, is determined. Then, the following formula isused to determine the ratio of the number of atoms of iron in the activegrowth material, or a precursor thereof, to the number of atoms of anyalkali metals in the active growth material, or a precursor thereof:

${r_{{iron}:{alkali}} = \frac{n_{{total}\mspace{14mu} {iron}}}{n_{{total}\mspace{14mu} {alkali}}}},$

where r_(iron:alkali) is the ratio of the number of atoms of iron in theactive growth material, or a precursor thereof, to the number of atomsof any alkali metals in the active growth material, or a precursorthereof; n_(total alkali) is the total number of alkali metal atoms inthe active growth material, or a precursor thereof; and n_(total iron)is the total number of iron atoms in the active growth material, or aprecursor thereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain iron or contains iron in an amount such that the ratioof the number of atoms of iron in the active growth material, or aprecursor thereof, to the number of atoms of any alkaline earth metalsin the active growth material, or a precursor thereof, is less than orequal to 3.5. In certain embodiments, the active growth material, or aprecursor thereof, contains iron in an amount such that the ratio of thenumber of atoms of iron in the active growth material, or a precursorthereof, to the number of atoms of any alkaline earth metals is lessthan or equal to 3.5, less than or equal to 3, less than or equal to2.5, less than or equal to 2, less than or equal to 1, less than orequal to 0.2, less than or equal to 0.1, less than or equal to 0.05, orless than or equal to 0.01. In some embodiments, the active growthmaterial, or a precursor thereof, contains iron in an amount such thatthe ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the number of atoms of any alkaline earthmetals is identically 0. Other ranges are also possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the number of atoms of any alkaline earthmetals in the active growth material, or a precursor thereof, can becalculated in the following manner. First, the total number of alkalineearth metal atoms in the active growth material, or a precursor thereof,is determined. After this step, the total number of iron atoms in theactive growth material, or a precursor thereof, is determined. Then, thefollowing formula is used to determine the ratio of the number of atomsof iron in the active growth material, or a precursor thereof, to thenumber of atoms of any alkaline earth metals in the active growthmaterial, or a precursor thereof:

${r_{{iron}:{{alkaline}\mspace{14mu} {earth}}} = \frac{n_{{total}\mspace{14mu} {iron}}}{n_{{total}\mspace{14mu} {al}\; {kaline}\mspace{14mu} {earth}}}},$

where r_(iron:alkaline earth) is the ratio of the number of atoms ofiron in the active growth material, or a precursor thereof, to thenumber of atoms of any alkali metals in the active growth material, or aprecursor thereof; n_(total alkaline earth) is the total number ofalkaline earth metal atoms in the active growth material, or a precursorthereof; and n_(total iron) is the total number of iron atoms in theactive growth material, or a precursor thereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain iron or contains iron in an amount such that the ratioof the number of atoms of iron in the active growth material, or aprecursor thereof, to the combined number of atoms of sodium andpotassium in the active growth material, or a precursor thereof, is lessthan or equal to 3.5. In certain embodiments, the active growthmaterial, or a precursor thereof, contains iron in an amount such thatthe ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the combined number of atoms of sodium andpotassium is less than or equal to 3.5, less than or equal to 3, lessthan or equal to 2.5, less than or equal to 2, less than or equal to 1,less than or equal to 0.2, less than or equal to 0.1, or less than orequal to 0.01. In some embodiments, the active growth material, or aprecursor thereof, contains iron in an amount such that the ratio of thenumber of atoms of iron in the active growth material, or a precursorthereof, to the combined number of atoms of sodium and potassium isidentically equal to 0. Other ranges are also possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the combined number of atoms of sodium andpotassium in the active growth material, or a precursor thereof, can becalculated in the following manner. First, the total number of sodiumatoms in the active growth material, or a precursor thereof, isdetermined. Then, the total number of potassium atoms in the activegrowth material, or a precursor thereof, is determined. After this step,the total number of iron atoms in the active growth material, or aprecursor thereof, is determined. Finally, the following formula is usedto determine the ratio of the number of atoms of iron in the activegrowth material, or a precursor thereof, to the combined number of atomsof sodium and potassium in the active growth material, or a precursorthereof:

${r_{{iron}:{{sodium}\mspace{14mu} {and}\mspace{14mu} {potassium}}} = \frac{n_{{total}\mspace{14mu} {iron}}}{n_{{total}\mspace{14mu} {sodium}} + n_{{total}\mspace{14mu} {potassium}}}},$

where r_(iron:sodium and potassium) is the ratio of the number of atomsof iron in the active growth material, or a precursor thereof, to thecombined number of atoms of sodium and potassium in the active growthmaterial, or a precursor thereof; n_(total sodium) is the total numberof sodium atoms in the active growth material, or a precursor thereof;n_(total potassium) is the total number of potassium atoms in the activegrowth material, or a precursor thereof; and n_(total iron) is the totalnumber of iron atoms in the active growth material, or a precursorthereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain iron or contains iron in an amount such that the ratioof the number of atoms of iron in the active growth material, or aprecursor thereof, to the number of atoms of sodium in the active growthmaterial, or a precursor thereof, is less than or equal to 3.5. Incertain embodiments, the active growth material, or a precursor thereof,contains iron in an amount such that the ratio of the number of atoms ofiron in the active growth material, or a precursor thereof, to thenumber of atoms of sodium is less than or equal to 3.5, less than orequal to 3, less than or equal to 2.5, less than or equal to 2, lessthan or equal to 1, less than or equal to 0.2, less than or equal to0.1, or less than or equal to 0.01.

In some embodiments, the active growth material, or a precursor thereof,contains iron in an amount such that the ratio of the number of atoms ofiron in the active growth material, or a precursor thereof, to thenumber of atoms of sodium is identically equal to 0. Other ranges arealso possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the number of atoms of sodium in the activegrowth material, or a precursor thereof, can be calculated in thefollowing manner. First, the total number of sodium atoms in the activegrowth material, or a precursor thereof, is determined. After this step,the total number of iron atoms in the active growth material, or aprecursor thereof, is determined. Then, the following formula is used todetermine the ratio of the number of atoms of iron in the active growthmaterial, or a precursor thereof, to the number of atoms sodium in theactive growth material, or a precursor thereof:

${r_{{{iron}:{sodium}}\;} = \frac{n_{{total}\mspace{14mu} {iron}}}{n_{{total}\mspace{14mu} {sodium}}}},$

where r_(iron:sodium) is the ratio of the number of atoms of iron in theactive growth material, or a precursor thereof, to the number of atomsof sodium in the active growth material, or a precursor thereof;n_(total sodium) is the total number of sodium atoms in the activegrowth material, or a precursor thereof; and n_(total iron) is the totalnumber of iron atoms in the active growth material, or a precursorthereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain iron or contains iron in an amount such that the ratioof the number of atoms of iron in the active growth material, or aprecursor thereof, to the number of atoms of potassium in the activegrowth material, or a precursor thereof, is less than or equal to 3.5.In certain embodiments, the active growth material, or a precursorthereof, contains iron in an amount such that the ratio of the number ofatoms of iron in the active growth material, or a precursor thereof, tothe number of atoms of potassium is less than or equal to 3.5, less thanor equal to 3, less than or equal to 2.5, less than or equal to 2, lessthan or equal to 1, less than or equal to 0.2, less than or equal to0.1, or less than or equal to 0.01. In some embodiments, the activegrowth material, or a precursor thereof, contains iron in an amount suchthat the ratio of the number of atoms of iron in the active growthmaterial, or a precursor thereof, to the number of atoms of potassium isidentically equal to 0. Other ranges are also possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the number of atoms of potassium in theactive growth material, or a precursor thereof, can be calculated in thefollowing manner. First, the total number of potassium atoms in theactive growth material, or a precursor thereof, is determined. Afterthis step, the total number of iron atoms in the active growth material,or a precursor thereof, is determined. Then, the following formula isused to determine the ratio of the number of atoms of iron in the activegrowth material, or a precursor thereof, to the number of atoms ofpotassium in the active growth material, or a precursor thereof:

${r_{{iron}:{potassium}} = \frac{n_{{total}\mspace{14mu} {iron}}}{n_{{total}\mspace{14mu} {potassium}}}},$

where r_(iron:potassium) is the ratio of the number of atoms of iron inthe active growth material, or a precursor thereof, to the number ofatoms of potassium in the active growth material, or a precursorthereof; n_(total potassium) is the total number of potassium atoms inthe active growth material, or a precursor thereof; and n_(total) ironis the total number of iron atoms in the active growth material, or aprecursor thereof.

According to some embodiments, the iron, when present, can be in the anyone or more of the following forms: elemental iron, a metal alloycontaining iron, and/or one or more iron salts. The iron can have anyoxidation state, including −4, −3, −2, 0, +1, +2, +3, +4, +5, and +6.Other oxidation states are also possible. The iron atoms contained inthe growth material can all have the same oxidation state, or can havedifferent oxidation states. One of ordinary skill in the art will beable to determine the iron content and iron state of a given activegrowth material, or a precursor thereof. For example, X-rayphotoelectron spectroscopy (XPS) may be used to determine thecomposition of an active growth material, or a precursor thereof. X-raydiffraction (XRD), optionally coupled with XPS, may be used to determinethe crystal structure of an active growth material, or a precursorthereof. Secondary ion mass spectroscopy (SIMS) can be used to determinechemical composition as a function of depth.

In some embodiments, the active growth material, or a precursor thereof,contains a relatively low amount of transition metals. For example, insome embodiments, the active growth material, or a precursor thereof,does not contain transition metals or contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the combinednumber of atoms of any alkali metals and any alkaline earth metals inthe active growth material, or a precursor thereof, is less than orequal to 3.5. The term “transition metals” is used herein to refer tothe following chemical elements: scandium, titanium, vanadium, chromium,manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium,niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver,cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium,platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium,hassium, meitnerium, ununnilium, unununium, and ununbium. In certainembodiments, the active growth material, or a precursor thereof,contains transition metals in an amount such that the ratio of thenumber of atoms of transition metals in the active growth material, or aprecursor thereof, to the combined number of atoms of any alkali metalsand alkaline earth metals in the active growth material, or a precursorthereof, is less than or equal to 3.5, less than or equal to 3, lessthan or equal to 2.5, less than or equal to 2, less than or equal to 1,less than or equal to 0.2, less than or equal to 0.1, or less than orequal to 0.01. In some embodiments, the active growth material, or aprecursor thereof, contains transition metals in an amount such that theratio of the number of atoms of transition metals in the active growthmaterial, or a precursor thereof, to the combined number of atoms of anyalkali metals and alkaline earth metals in the active growth material,or a precursor thereof, is identically equal to 0. Other ranges are alsopossible.

The ratio of the total number of atoms of transition metals in theactive growth material, or a precursor thereof, to the combined numberof atoms of any alkali metals and alkaline earth metals in the activegrowth material, or a precursor thereof, can be calculated in thefollowing manner. First, the total number of alkali metal atoms in theactive growth material, or a precursor thereof, is determined. Then, thetotal number of alkaline earth metal atoms in the active growthmaterial, or a precursor thereof, is determined. After this step, thetotal number of transition metals atoms in the active growth material,or a precursor thereof, is determined. Finally, the following formula isused to determine the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the combinednumber of atoms of any alkali metals and alkaline earth metals in theactive growth material, or a precursor thereof:

${r_{t{ransition}\mspace{14mu} {{metals}:{{alkali}\mspace{14mu} {and}\mspace{14mu} {alkaline}}}} = \frac{n_{{total}\mspace{14mu} {transition}\mspace{14mu} {metals}}}{n_{{total}\mspace{14mu} {alkaline}\mspace{14mu} {earth}} + n_{{total}\mspace{14mu} {alkali}}}},$

where r_(transition metals:alkali and alkaline) is the ratio of thenumber of atoms of transition metals in the active growth material, or aprecursor thereof, to the combined number of atoms of any alkali metalsand alkaline earth metals in the active growth material, or a precursorthereof; n_(total alkaline earth) is the total number of alkaline earthmetal atoms in the active growth material, or a precursor thereof;n_(total alkali) is the total number of alkali metal atoms in the activegrowth material, or a precursor thereof; and n_(total transition metals)is the total number of transition metals atoms in the active growthmaterial, or a precursor thereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain transition metals or contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the number ofatoms of any alkali metals in the active growth material, or a precursorthereof, is less than or equal to 3.5. In certain embodiments, theactive growth material, or a precursor thereof, contains transitionmetals in an amount such that the ratio of the number of atoms oftransition metals in the active growth material, or a precursor thereof,to the number of atoms of any alkali metals is less than or equal to3.5, less than or equal to 3, less than or equal to 2.5, less than orequal to 2, less than or equal to 1, less than or equal to 0.2, lessthan or equal to 0.1, or less than or equal to 0.01. In someembodiments, the active growth material, or a precursor thereof,contains transition metals in an amount such that the ratio of thenumber of atoms of transition metals in the active growth material, or aprecursor thereof, to the number of atoms of any alkali metals isidentically equal to 0. Other ranges are also possible.

The ratio of the number of atoms of iron in the active growth material,or a precursor thereof, to the number of atoms of any alkali metals inthe active growth material, or a precursor thereof, can be calculated inthe following manner. First, the total number of alkali metal atoms inthe active growth material, or a precursor thereof, is determined. Afterthis step, the total number of transition metals atoms in the activegrowth material, or a precursor thereof, is determined. Then, thefollowing formula is used to determine the ratio of the number of atomsof transition metals in the active growth material, or a precursorthereof, to the number of atoms of any alkali metals in the activegrowth material, or a precursor thereof:

${r_{t{ransition}\mspace{14mu} {{metals}:{alkali}}} = \frac{n_{{total}\mspace{14mu} {transition}\mspace{14mu} {metals}}}{n_{{total}\mspace{14mu} {alkali}}}},$

where r_(transition metals:alkali) is the ratio of the number of atomsof transition metals in the active growth material, or a precursorthereof, to the number of atoms of any alkali metals in the activegrowth material, or a precursor thereof; n_(total alkali) is the totalnumber of alkali metal atoms in the active growth material, or aprecursor thereof; and n_(total transition metals) is the total numberof transition metals atoms in the active growth material, or a precursorthereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain transition metals or contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the number ofatoms of any alkaline earth metals in the active growth material, or aprecursor thereof, is less than or equal to 3.5. In certain embodiments,the active growth material, or a precursor thereof, contains transitionmetals in an amount such that the ratio of the number of atoms oftransition metals in the active growth material, or a precursor thereof,to the number of atoms of any alkaline earth metals is less than orequal to 3.5, less than or equal to 3, less than or equal to 2.5, lessthan or equal to 2, less than or equal to 1, less than or equal to 0.2,less than or equal to 0.1, or less than or equal to 0.01. In someembodiments, the active growth material, or a precursor thereof,contains transition metals in an amount such that the ratio of thenumber of atoms of transition metals in the active growth material, or aprecursor thereof, to the number of atoms of any alkaline earth metalsis identically equal to 0. Other ranges are also possible.

The ratio of the number of atoms of transition metals in the activegrowth material, or a precursor thereof, to the number of atoms of anyalkaline earth metals in the active growth material, or a precursorthereof, can be calculated in the following manner. First, the totalnumber of alkaline earth metal atoms in the active growth material, or aprecursor thereof, is determined. After this step, the total number oftransition metals atoms in the active growth material, or a precursorthereof, is determined. Then, the following formula is used to determinethe ratio of the number of atoms of transition metals in the activegrowth material, or a precursor thereof, to the number of atoms of anyalkaline earth metals in the active growth material, or a precursorthereof:

${r_{t{ransition}\mspace{14mu} {{metals}:{{alkaline}\mspace{14mu} {earth}}}} = \frac{n_{{total}\mspace{14mu} {transition}\mspace{14mu} {metals}}}{n_{{total}\mspace{14mu} {alkaline}\mspace{14mu} {earth}}}},$

where r_(transition metals:alkaline earth) is the ratio of the number ofatoms of transition metals in the active growth material, or a precursorthereof, to the number of atoms of any alkaline earth metals in theactive growth material, or a precursor thereof; n_(total alkaline earth)is the total number of alkaline earth metal atoms in the active growthmaterial, or a precursor thereof; and n_(total transition metals) is thetotal number of transition metals atoms in the active growth material,or a precursor thereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain transition metals or contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the combinednumber of atoms of sodium and potassium in the active growth material,or a precursor thereof, is less than or equal to 3.5. In certainembodiments, the active growth material, or a precursor thereof,contains transition metals in an amount such that the ratio of thenumber of atoms of transition metals in the active growth material, or aprecursor thereof, to the combined number of atoms of sodium andpotassium is less than or equal to 3.5, less than or equal to 3, lessthan or equal to 2.5, less than or equal to 2, less than or equal to 1,less than or equal to 0.2, less than or equal to 0.1, or less than orequal to 0.01. In some embodiments, the active growth material, or aprecursor thereof, contains transition metals in an amount such that theratio of the number of atoms of transition metals in the active growthmaterial, or a precursor thereof, to the combined number of atoms ofsodium and potassium is identically equal to 0. Other ranges are alsopossible.

The ratio of the number of atoms of transition metals in the activegrowth material, or a precursor thereof, to the combined number of atomsof sodium and potassium in the active growth material, or a precursorthereof, can be calculated in the following manner. First, the totalnumber of sodium atoms in the active growth material, or a precursorthereof, is determined. Then, the total number of potassium atoms in theactive growth material, or a precursor thereof, is determined. Afterthis step, the total number of transition metals atoms in the activegrowth material, or a precursor thereof, is determined. Finally, thefollowing formula is used to determine the ratio of the number of atomsof transition metals in the active growth material, or a precursorthereof, to the combined number of atoms of sodium and potassium in theactive growth material, or a precursor thereof:

${r_{{transition}\mspace{14mu} {{metals}:{{sodium}\mspace{14mu} {and}\mspace{14mu} {potassium}}}} = \frac{n_{{total}\mspace{14mu} {transition}\mspace{14mu} {metals}}}{n_{{total}\mspace{14mu} {sodium}} + n_{{total}\mspace{14mu} {potassium}}}},$

where r_(transition metals:sodium and potassium) is the ratio of thenumber of atoms of transition metals in the active growth material, or aprecursor thereof, to the combined number of atoms of sodium andpotassium in the active growth material, or a precursor thereof;n_(total sodium) is the total number of sodium atoms in the activegrowth material, or a precursor thereof; n_(total potassium) is thetotal number of potassium atoms in the active growth material, or aprecursor thereof; and n_(total transition metals) is the total numberof transition metals atoms in the active growth material, or a precursorthereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain transition metals or contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the number ofatoms of sodium in the active growth material, or a precursor thereof,is less than or equal to 3.5. In certain embodiments, the active growthmaterial, or a precursor thereof, contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the number ofatoms of sodium is less than or equal to 3.5, less than or equal to 3,less than or equal to 2.5, less than or equal to 2, less than or equalto 1, less than or equal to 0.2, less than or equal to 0.1, or less thanor equal to 0.01. In some embodiments, the active growth material, or aprecursor thereof, contains transition metals in an amount such that theratio of the number of atoms of transition metals in the active growthmaterial, or a precursor thereof, to the number of atoms of sodium isidentically equal to 0. Other ranges are also possible.

The ratio of the number of atoms of transition metals in the activegrowth material, or a precursor thereof, to the number of atoms ofsodium in the active growth material, or a precursor thereof, can becalculated in the following manner. First, the total number of sodiumatoms in the active growth material, or a precursor thereof, isdetermined. After this step, the total number of transition metals atomsin the active growth material, or a precursor thereof, is determined.Then, the following formula is used to determine the ratio of the numberof atoms of transition metals in the active growth material, or aprecursor thereof, to the number of atoms sodium in the active growthmaterial, or a precursor thereof:

${r_{t{ransition}\mspace{14mu} {{metals}:{sodium}}} = \frac{n_{{total}\mspace{14mu} {transition}\mspace{14mu} {metals}}}{n_{{total}\mspace{14mu} {sodium}}}},$

where r_(transition metals:sodium) is the ratio of the number of atomsof transition metals in the active growth material, or a precursorthereof, to the number of atoms of sodium in the active growth material,or a precursor thereof; n_(total sodium) is the total number of sodiumatoms in the active growth material, or a precursor thereof; andn_(total transition metals) is the total number of transition metalsatoms in the active growth material, or a precursor thereof.

In some embodiments, the active growth material, or a precursor thereof,does not contain transition metals or contains transition metals in anamount such that the ratio of the number of atoms of transition metalsin the active growth material, or a precursor thereof, to the number ofatoms of potassium in the active growth material, or a precursorthereof, is less than or equal to 3.5. In certain embodiments, theactive growth material, or a precursor thereof, contains transitionmetals in an amount such that the ratio of the number of atoms oftransition metals in the active growth material, or a precursor thereof,to the number of atoms of potassium is less than or equal to 3.5, lessthan or equal to 3, less than or equal to 2.5, less than or equal to 2,less than or equal to 1, less than or equal to 0.2, less than or equalto 0.1, or less than or equal to 0.01. In some embodiments, the activegrowth material, or a precursor thereof, contains transition metals inan amount such that the ratio of the number of atoms of transitionmetals in the active growth material, or a precursor thereof, to thenumber of atoms of potassium is identically equal to or 0. Other rangesare also possible.

The ratio of the number of atoms of transition metals in the activegrowth material, or a precursor thereof, to the number of atoms ofpotassium in the active growth material, or a precursor thereof, can becalculated in the following manner. First, the total number of potassiumatoms in the active growth material, or a precursor thereof, isdetermined. After this step, the total number of transition metals atomsin the active growth material, or a precursor thereof, is determined.Then, the following formula is used to determine the ratio of the numberof atoms of transition metals in the active growth material, or aprecursor thereof, to the number of atoms sodium in the active growthmaterial:

${r_{t{ransition}\mspace{14mu} {{metals}:{potassium}}} = \frac{n_{{total}\mspace{14mu} {transition}\mspace{14mu} {metals}}}{n_{{total}\mspace{14mu} {potassium}}}},$

where r_(transition metals:potassium) is the ratio of the number ofatoms of transition metals in the active growth material, or a precursorthereof, to the number of atoms of potassium in the active growthmaterial, or a precursor thereof; n_(total potassium) is the totalnumber of potassium atoms in the active growth material, or a precursorthereof; and n_(total transition metals) is the total number oftransition metals atoms in the active growth material, or a precursorthereof.

According to some embodiments, the transition metals in the activegrowth material, or a precursor thereof, when present, can be in the anyone or more of the following forms: elemental transition metals, a metalalloy containing one or more transition metals, and/or one or moretransition metal salts. The transition metals, when present in theactive growth material, or a precursor thereof, can have any oxidationstate, including −4, −3, −2, 0, +1, +2, +3, +4, +5, +6, and +7. Otheroxidation states are also possible. The transition metal atoms containedin the growth material can all have the same oxidation state, or canhave different oxidation states. One of ordinary skill in the art willbe able to determine the transition metal content and transition metalstate of a given active growth material, or a precursor thereof. Forexample, X-ray photoelectron spectroscopy (XPS) may be used to determinethe composition of an active growth material, or a precursor thereof.X-ray diffraction (XRD), optionally coupled with XPS, may be used todetermine the crystal structure of an active growth material, or aprecursor thereof. Secondary ion mass spectroscopy (SIMS) can be used todetermine chemical composition as a function of depth.

In certain embodiments, a relatively large proportion of the atoms ofthe active growth material, or a precursor thereof, are alkaline earthmetals and/or alkali metals. In some embodiments, greater than or equalto 50%, greater than or equal to 75%, greater than or equal to 90%,greater than or equal to 95%, or greater than or equal to 99% of theatoms of the active growth material, or a precursor thereof, arealkaline earth metals and/or alkali metals. According to certainembodiments, less than or equal to 100%, less than or equal to 99%, lessthan or equal to 95%, less than or equal to 90%, or less than or equalto 75% of the atoms comprising the active growth material, or aprecursor thereof, are alkaline earth metals and/or alkali metals.Combinations of the above-referenced ranges are also possible. Otherranges are also possible.

According to certain embodiments, at least 50% of the carbon-basednanostructures that are grown are in direct contact with at least one ofan alkali metal and an alkaline earth metal (e.g., during the growthprocess and/or immediately following the growth process). In certainembodiments, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95%, at least 99%, or all of the carbon-based nanostructures thatare grown are in direct contact with the at least one of an alkali metaland an alkaline earth metal (e.g., during the growth process orimmediately following the growth process). In certain embodiments, atleast 60%, at least 70%, at least 80%, at least 90%, at least 95%, atleast 99%, or all of the carbon-based nanostructures that are grown arein direct contact with the alkaline earth metal (e.g., during the growthprocess or immediately following the growth process). In certainembodiments, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95%, at least 99%, or all of the carbon-based nanostructures thatare grown are in direct contact with the alkali metal (e.g., during thegrowth process or immediately following the growth process). In certainembodiments, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95%, at least 99%, or all of the carbon-based nanostructures thatare grown are in direct contact with at least one of sodium andpotassium (e.g., during the growth process or immediately following thegrowth process). In certain embodiments, at least 60%, at least 70%, atleast 80%, at least 90%, at least 95%, at least 99%, or all of thecarbon-based nanostructures that are grown are in direct contact withsodium (e.g., during the growth process or immediately following thegrowth process). In certain embodiments, at least 60%, at least 70%, atleast 80%, at least 90%, at least 95%, at least 99%, or all of thecarbon-based nanostructures that are grown are in direct contact withpotassium (e.g., during the growth process or immediately following thegrowth process). The carbon-based nanostructure can contact the alkalimetal or alkaline earth metal in a manner such that the alkali metal oralkaline earth metal is located between the carbon-based nanostructuresand an optional substrate, in some embodiments. In some embodiments, thecarbon-based nanostructures can contact the alkali metal or alkalineearth metal in a manner such that the carbon-based nanostructure is inbetween the alkali metal or alkaline earth metal and an optionalsubstrate.

Generally, materials which are in direct contact with each other aredirectly adjacent to each other with no intervening material.

In some embodiments, the growth of at least 50% of the carbon-basednanostructures is activated by at least one of an alkali metal and analkaline earth metal. In certain embodiments, the growth of at least75%, at least 90%, at least 95%, or at least 99% of the carbon-basednanostructures is activated by at least one of an alkali metal and analkaline earth metal. According to certain embodiments, the growth of100% of the carbon-based nanostructures is activated by at least one ofan alkali metal and an alkaline earth metal. In certain embodiments,activation comprises reducing the energy barrier between the state ofthe carbon atoms of the precursor prior to incorporation into thecarbon-based nanostructure and the state of the carbon atoms of theprecursor after incorporation into the carbon-based nanostructure.Activation can comprise a substantial acceleration of the rate of growthin certain embodiments. In some embodiments, activation can cause growthto occur under conditions where growth would not occur or besignificantly retarded in the absence of activation. One of ordinaryskill in the art would be capable of determining the effect of thepresence of a particular material on the activity of carbon-basednanostructure growth by, for example, determining the number ofcarbon-based nanostructures grown in the presence of the particularmaterial, determining the number of carbon-based nanostructures grown inthe absence of the particular material but under otherwise essentiallyidentical conditions, and comparing the two amounts.

Certain, but not necessarily all, of the active growth materialsdescribed herein may possess advantages compared to other materials. Forexample, the active growth materials described herein can be capable ofpromoting nanostructure growth on challenging substrates, such aspolymers, carbon, metals, and ceramics. As one example, active growthmaterials described herein can, according to certain embodiments,promote nanostructure growth on sized carbon fiber substrates. Theactive growth materials described herein may also be resistant to oxideformation, in some embodiments. The active growth materials describedherein may promote growth at low temperatures, according to certainembodiments.

In some embodiments, the active growth material, or a precursor thereof,is deposited on an optional growth substrate from a liquid containingactive growth material (or active material precursor) particles. Notwishing to be bound by any particular theory, the manner in which theactive growth material, or a precursor thereof, leaves the liquid and isdeposited onto the substrate might enhance the activity of the activegrowth material towards carbon nanostructure growth. For example, insome cases, an enhancement in active growth material activity mightoccur due to clustering of a relatively large number of active growthmaterial (or active growth material precursor) particles. In someinstances, an enhancement in active growth material activity might arisedue to a change in surface morphology of one or more active growthmaterial particles and/or due to a doping effect resulting fromco-deposition of active growth material particles and dopants from theliquid.

In some embodiments, the active growth material, or a precursor thereof,may be deposited on an optional growth substrate by a vapor depositionprocess. For instance, the active growth material, or a precursorthereof, may be deposited by one or more of sputtering and/orevaporative deposition. In some embodiments, a vapor deposition processmay be followed by one or more additional processes to formnanoparticles. The additional processes may include at least one or bothof application of heat to the active growth material or precursorthereof and/or exposure of the active growth material or a precursorthereof to a chemical.

A plurality of active growth material particles, or particles of activegrowth material precursor, can be organized into a monolayer ormultilayer film, in some instances. A monolayer or multilayer film mightbe prepared, for example, using the Langmuir-Schaffer orLangmuir-Blodgett methods. As a specific example, prefabricatednanoparticles can be dispersed in a carrier fluid (e.g., toluene), whichcan then be transferred (e.g., via a pipette) as a thin layer ontoanother layer of fluid (e.g., water). The carrier fluid can then beevaporated away leaving behind a film of nanoparticles. The film canthen be transferred onto a substrate and used to grow carbon-basednanostructures.

In some cases, the active growth material, or a precursor thereof, maycomprise a plurality of nanoscale features. As used herein, a “nanoscalefeature” refers to a feature, such as a protrusion, groove orindentation, particle, or other measurable geometric feature on anarticle that has at least one cross-sectional dimension of less than 1micron. In some cases, the nanoscale feature may have at least onecross-sectional dimension of less than 500 nm, less than 250 nm, lessthan 100 nm, less than 10 nm, less than 5 nm, less than 3 nm, less than2 nm, less than 1 nm, between 0.3 and 10 nm, between 10 nm and 100 nm,or between 100 nm and 1 micron. Not wishing to be bound by any theory,the nanoscale feature may increase the rate at which a reaction,nucleation step, or other process involved in the formation of ananostructure occurs. Nanoscale features can be formed, for example, byroughening the surface of an active growth material, or a precursorthereof.

The active growth material, or a precursor thereof, can comprise oneparticle or can comprise multiple particles. Any active growth materialparticles (or precursor particles) can have any size. In someembodiments, one or more active growth material particles (or precursorparticles) has nanoscale dimensions for one or more of their length,width, and depth. Active growth material particles (or active growthmaterial precursor particles) can be nanoparticles, nanowires, and/orthin films. In some instances, the active growth material, or aprecursor thereof, may comprise nanoparticles. Generally, the term“nanoparticle” is used to refer to any particle having a maximumcross-sectional dimension of less than 1 micron. In some embodiments, anactive growth material nanoparticle or active growth material precursornanoparticle may have a maximum cross-sectional dimension of less than500 nm, less than 250 nm, less than 100 nm, less than 10 nm, less than 5nm, less than 3 nm, less than 2 nm, less than 1 nm, between 0.3 and 10nm, between 10 nm and 100 nm, or between 100 nm and 1 micron. Aplurality of active growth material nanoparticles or active growthmaterial precursor nanoparticles may, in some cases, have an averagemaximum cross-sectional dimension of less than 1 micron, less than 100nm, less than 10 nm, less than 5 nm, less than 3 nm, less than 2 nm,less than 1 nm, between 0.3 and 10 nm, between 10 nm and 100 nm, orbetween 100 nm and 1 micron. As used herein, the “maximumcross-sectional dimension” refers to the largest distance between twoopposed boundaries of an individual structure that may be measured. The“average maximum cross-sectional dimension” of a plurality of structuresrefers to the number average. In accordance with certain embodiments,one or more active growth material particles or active growth materialprecursor particles can have micrometer or larger dimensions for one ormore of their length, width, and depth.

The active growth material, or a precursor thereof, may have any shape.Non-limiting examples of acceptable shapes include spheres, cylinders,cubes, and parallelepipeds. In certain embodiments, the active growthmaterial, or a precursor thereof, may be faceted. The active growthmaterial, or a precursor thereof, may have morphologies with low or nosymmetry in some embodiments. Active growth materials or active growthmaterial precursors which form nanowires may have cross-sectionals thatare circular, triangular, square, rectangular, pentagonal, hexagonal,heptagonal, octagonal, etc. In other embodiments, active growthmaterials or active growth material precursors which form nanowires mayhave cross-sections that have low or no symmetry. In certain embodimentsin which active growth material particles or active growth materialprecursor particles are used, all of the active growth materialparticles or active growth material precursor particles may have thesame or substantially similar morphologies. In other embodiments, theactive growth material particles or active growth material precursorparticles may comprise different or substantially differentmorphologies. In some instances, the active growth material, or aprecursor thereof, may be deposited on an optional growth substrate in apattern (e.g., lines, dots, or any other suitable form).

In some instances in which the active growth material (or precursorthereof) is in particulate form, the particles may be substantially thesame shape and/or size (“monodisperse”). For example, the particles mayhave a distribution of dimensions such that the standard deviation ofthe maximum cross-sectional dimensions of the particles is no more than50%, no more than 25%, no more than 10%, no more than 5%, no more than2%, or no more than 1% of the average maximum cross-sectional dimensionsof the particles. Standard deviation (lower-case sigma) is given itsnormal meaning in the art, and may be calculated as:

$\sigma = \sqrt{\frac{\sum\limits_{i = 1}^{n}\left( {D_{i} - D_{avg}} \right)^{2}}{n - 1}}$

wherein D_(i) is the maximum cross-sectional dimension of particle i,D_(avg) is the average of the cross-sectional dimensions of theparticles, and n is the number of particles. The percentage comparisonsbetween the standard deviation and the average maximum cross-sectionaldimensions of the particles outlined above can be obtained by dividingthe standard deviation by the average and multiplying by 100%.

The active growth material, or a precursor thereof, may have any atomicarrangement. In some embodiments, the active growth material, or aprecursor thereof, may comprise particles or other forms which aresingle crystalline, polycrystalline, and/or amorphous. In certainembodiments, each particle of active growth material or active growthmaterial precursor has the same atomic structure. In other embodiments,different particles of active growth material or active growth materialprecursor may have different atomic structures.

In some cases, the active growth material, or a precursor thereof, is incontact with a portion of a growth substrate comprising a material thatis different from the material from which the active growth material, ora precursor thereof, is made (e.g., the portion of the active growthmaterial, or a precursor thereof, in contact with the growth substrate).In some cases the active growth material, or a precursor thereof, is incontact with a portion of a growth substrate comprising a material thatis the same as the material from which the active growth material, or aprecursor thereof, is made (e.g., the portion of the active growthmaterial, or a precursor thereof, in contact with the growth substrate).

As noted above, carbon-based nanostructures can be grown by exposing theactive growth material to one or more precursors of the carbon-basednanostructures. The precursor(s) can, according to certain embodiments,participate in a chemical reaction in which carbon dissociates from theprecursor and forms new covalent bonds to grow the carbon-basednanostructures.

According to some embodiments, the nanostructure precursor is present inthe gas phase prior to being incorporated into the carbon-basednanostructure. For example, according to certain embodiments, gaseousacetylene and/or carbon dioxide can be used as carbon-basednanostructure precursors. The precursor of the carbon-basednanostructures need not necessarily be in the gaseous phase, however,and in certain embodiments, the precursor is in the solid and/or liquidphase (in addition to, or in place of, a gas phase precursor). Incertain embodiments that comprise more than one precursor, eachprecursor may be in one or more phases. Different precursors may be inthe same phase(s) or may be in different phases.

According to some embodiments, the precursor comprises carbon dioxide(CO₂). The carbon dioxide in the precursor can be in any state ofmatter, including solid, liquid, and/or gas. In certain, although notnecessarily all, embodiments, a gaseous carbon dioxide precursor isused. The carbon dioxide can be in more than one of these forms, e.g.,when the reaction conditions comprise a temperature and pressure whenmore than one phase of carbon dioxide is stable. In some embodiments,carbon dioxide is the only precursor present. In other embodiments,carbon dioxide is one of two or more precursors to which the activegrowth material is exposed. Without wishing to be bound by anyparticular theory, it has been observed that the use of carbon dioxideprecursors can allow one to grow carbon-based nanostructures (e.g.,carbon nanotubes) at relatively low temperatures, compared to thetemperatures at which carbon-based nanostructures can be grown in theabsence of the carbon dioxide but under otherwise essentially identicalconditions.

According to some embodiments, the precursor comprises at least one of ahydrocarbon and an alcohol. In certain embodiments, the precursor maycontain one or more hydrocarbons but no alcohols. In other embodiments,the precursor may contain one or more alcohols but no hydrocarbons. Inyet other embodiments, the precursor may contain both one or morehydrocarbons and one or more alcohols. In some such embodiments, thehydrocarbon(s) and/or alcohol(s) are the only precursors present. Inother embodiments, the precursor further comprises additional molecules.For example, in some embodiments, the precursor comprises carbon dioxidein addition to a hydrocarbon and/or an alcohol. In one particular set ofembodiments, the precursor comprises at least one alkyne (e.g.,acetylene) and carbon dioxide.

The term “hydrocarbon” is used herein to describe organic compoundsconsisting only of hydrogen and carbon. A hydrocarbon may be saturatedor unsaturated (at one or more locations) and may have a linear,branched, monocyclic, or polycyclic structure. A hydrocarbon may bealiphatic or aromatic, and may contain one or more alkyl, alkene, and/oralkyne functional groups. In certain embodiments, the hydrocarbon is analkane. In some embodiments, the hydrocarbon is an alkene. In certainembodiments, the hydrocarbon is an alkyne. In some embodiments, thehydrocarbon is a C₁-C₁₀ hydrocarbon, such as a C₁-C₈ hydrocarbon, aC₁-C₆ hydrocarbon, or a C₁-C₄ hydrocarbon. For example, in someembodiments, the hydrocarbon is a C₁-C₁₀ alkyne, a C₁-C₈ alkyne, a C₁-C₆alkyne, or a C₁-C₄ alkyne. In some embodiments, the hydrocarbon is aC₁-C₁₀ alkane, a C₁-C₈ alkane, a C₁-C₆ alkane, or a C₁-C₄ alkane. Incertain embodiments, the hydrocarbon is a C₁-C₁₀ alkene, a C₁-C₈ alkene,a C₁-C₆ alkene, or a C₁-C₄ alkene. The hydrocarbon may have anymolecular weight. Non-limiting examples of suitable hydrocarbons includemethane (CH₄), ethylene (C₂H₄), and acetylene (C₂H₂). In certain but notnecessarily all embodiments, the hydrocarbon comprises acetylene.

As used herein, the term “alcohol” refers to a molecule with at leastone hydroxyl (—OH) functional group. Non-limiting examples of alcoholsinclude methanol, ethanol, (iso)propanol, and butanol. Alcohols may besaturated or unsaturated (at one or more locations) and may have alinear, branched, monocyclic, or polycyclic structure. Alcohols may bealiphatic or aromatic, and may contain one or more alkyl, alkene, and/oralkyne functional groups. In certain but not necessarily allembodiments, alcohols may comprise more than one —OH functional group.In some embodiments, the alcohol is a C₁-C₁₀ alcohol, such as a C₁-C₈alcohol, a C₁-C₆ alcohol, or a C₁-C₄ alcohol.

In some embodiments, at least 50% of the nanostructure precursor is madeup of a combination of hydrocarbons, alcohols, and carbon dioxide. Incertain embodiments, at least 60%, at least 70%, at least 80%, at least90%, at least 95%, at least 99%, or all of the nanostructure precursoris made up of a combination of hydrocarbons, alcohols, and carbondioxide. In certain embodiments, at least 50%, at least 60%, at least70%, at least 80%, at least 90%, at least 95%, at least 99%, or all ofthe nanostructure precursor is made up of a combination of hydrocarbonsand carbon dioxide. In certain embodiments, at least 60%, at least 70%,at least 80%, at least 90%, at least 95%, at least 99%, or all of thenanostructure precursor is made up of a combination of alkynes (e.g.,C₁-C₁₀, C₁-C₈, C₁-C₆, or C₁-C₄ alkynes) and carbon dioxide. In certainembodiments, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95%, at least 99%, or all of the nanostructure precursor is madeup of a combination of acetylene and carbon dioxide. Other ranges arealso possible.

As noted above, the nanostructure precursor material can be in anysuitable phase. In one set of embodiments, the nanostructure precursormaterial comprises a solid. Examples of solid precursor materialsinclude, for example, coal, coke, amorphous carbon, unpyrolyzed organicpolymers (e.g., phenol-formaldehyde, resorcinol-formaldehyde,melamine-formaldehyde, etc.), partially pyrolyzed organic polymers,diamond, graphene, graphite, or any other suitable solid form of carbon.In some embodiments, the solid precursor material may contain carbon inan amount of at least 25 wt %, at least 50 wt %, at least 75 wt %, atleast 85 wt %, at least 90 wt %, at least 95 wt %, at least 98 wt %, orat least 99 wt %.

In one set of embodiments, the nanostructure precursor materialcomprises both a solid and a non-solid (e.g., a liquid, a gas, etc.).For example, the nanostructure precursor material can comprise a solidform of carbon placed close to or in contact with the active growthmaterial and a vapor-phase precursor material. As a specific example,the solid precursor component can be deposited on or near the activegrowth material as soot, amorphous carbon, graphene, or graphite, andthe active growth material can be exposed to vapor comprising ahydrocarbon (e.g., methane, ethylene, acetylene, and the like). Notwishing to be bound by any particular theory, under some growthconditions, the presence of the solid precursor material can allow fornanostructure growth that might not occur in the absence of the solidprecursor material. In some cases, the solid precursor material mightprovide a base from which the non-solid nanostructure precursor materialcan be added to grow the carbon-based nanostructure. For example, insome embodiments, a small portion of a carbon nanotube can be used as astarting material from which a larger nanotube can be grown usingnon-solid carbon nanostructure precursor material.

As noted above, certain embodiments comprise exposing the nanostructureprecursor and the active growth material to a set of conditions thatcauses growth of carbon-based nanostructures on the active growthmaterial. In some cases, the set of conditions may facilitate nucleationof carbon-based nanostructures during the growth process. According tocertain embodiments, carbon-based nanostructures can be grown atrelatively low temperatures. The ability to grow carbon-basednanostructures at relatively low temperatures can be advantageous,according to certain but not necessarily all embodiments, as the use oflow temperatures can reduce the amount of energy needed to perform thegrowth process. According to some embodiments, the active growthmaterial is at a temperature of less than or equal to 500° C. during thegrowth of the carbon-based nanostructures. In certain embodiments, theactive growth material is at a temperature of less than or equal to 475°C. during the growth of the carbon-based nanostructures. The temperatureof the active growth material may be less than or equal to 450° C., lessthan or equal to 425° C., less than or equal to 400° C., less than orequal to 350° C., less than or equal to 300° C., less than or equal to250° C., less than or equal to 200° C., less than or equal to 150° C.,or less than or equal to 100° C. during the growth of the carbon-basednanostructures, according to certain embodiments. The temperature of theactive growth material during the growth of the carbon-basednanostructures may be greater than or equal to 50° C., greater than orequal to 100° C., greater than or equal to 150° C., greater than orequal to 200° C., greater than or equal to 250° C., greater than orequal to 300° C., greater than or equal to 350° C., or greater than orequal to 400° C., according to certain embodiments. Combinations of theabove referenced ranges are also possible (for example, greater than orequal to 100° C. and less than or equal to 500° C.). Other ranges arealso possible.

In some embodiments, the precursor of the carbon-based nanostructures isat a temperature of less than or equal to 500° C. during the growth ofthe carbon-based nanostructures. In certain embodiments, the precursorof the carbon-based nanostructures is at a temperature of less than orequal to 475° C. during the growth of the carbon-based nanostructures.In some embodiments, the temperature of the precursor of thecarbon-based nanostructures may be less than or equal to 450° C., lessthan or equal to 425° C., less than or equal to 400° C., less than orequal to 350° C., less than or equal to 300° C., less than or equal to250° C., less than or equal to 200° C., less than or equal to 150° C.,or less than or equal to 100° C. during the growth of the carbon-basednanostructures. The temperature of the precursor of the carbon-basednanostructures during the growth of the carbon-based nanostructures maybe greater than or equal to 50° C., greater than or equal to 100° C.,greater than or equal to 150° C., greater than or equal to 200° C.,greater than or equal to 250° C., greater than or equal to 300° C.,greater than or equal to 350° C., or greater than or equal to 400° C.,according to certain embodiments. Combinations of the above referencedranges are also possible (for example, greater than or equal to 100° C.and less than or equal to 500° C.). Other ranges are also possible. Insome embodiments, the precursor of the carbon-based nanostructures is ata temperature outside the ranges listed above during the growth of thecarbon-based nanostructures.

In certain embodiments, the substrate (when present) is at a temperatureof less than or equal to 500° C. during the growth of the carbon-basednanostructures. In certain embodiments, the substrate (when present) isat a temperature of less than or equal to 475° C. during the growth ofthe carbon-based nanostructures. The temperature of the substrate (whenpresent) may be less than or equal to 450° C., less than or equal to425° C., less than or equal to 400° C., less than or equal to 350° C.,less than or equal to 300° C., less than or equal to 250° C., less thanor equal to 200° C., less than or equal to 150° C., or less than orequal to 100° C. during the growth of the carbon-based nanostructures,according to certain embodiments. The temperature of the substrate (whenpresent) during the growth of the carbon-based nanostructures may begreater than or equal to 50° C., greater than or equal to 100° C.,greater than or equal to 150° C., greater than or equal to 200° C.,greater than or equal to 250° C., greater than or equal to 300° C.,greater than or equal to 350° C., or greater than or equal to 400° C.,according to certain embodiments. Combinations of the above referencedranges are also possible (for example, greater than or equal to 100° C.and less than or equal to 500° C.). Other ranges are also possible.

According to certain embodiments, carbon-based nanostructure growth canoccur within a vessel within which the temperature of the enclosed spaceis less than or equal to 500° C. during the growth of the carbon-basednanostructures, according to certain embodiments. In certainembodiments, the enclosed space is at a temperature of less than orequal to 475° C. during the growth of the carbon-based nanostructures.The temperature of the enclosed space may be less than or equal to 450°C., less than or equal to 425° C., less than or equal to 400° C., lessthan or equal to 350° C., less than or equal to 300° C., less than orequal to 250° C., less than or equal to 200° C., less than or equal to150° C., or less than or equal to 100° C. during the growth of thecarbon-based nanostructures, according to certain embodiments. Thetemperature of the enclosed space during the growth of the carbon-basednanostructures may be greater than or equal to 50° C., greater than orequal to 100° C., greater than or equal to 150° C., greater than orequal to 200° C., greater than or equal to 250° C., greater than orequal to 300° C., greater than or equal to 350° C., or greater than orequal to 400° C., according to certain embodiments. Combinations of theabove referenced ranges are also possible (for example, greater than orequal to 100° C. and less than or equal to 500° C.). Other ranges arealso possible.

In certain embodiments, two or more of the active growth material, thesubstrate (when present), the precursor, and the vessel (when present)are at the same temperature. According to some embodiments, none of theactive growth material, substrate, precursor, and vessel are at the sametemperature. The temperature of any one or more components is higher orlower before and/or after growth for any period of time, in someembodiments.

In some cases, a source of external energy may be coupled with thegrowth apparatus to provide energy to cause the growth sites to reachthe necessary temperature for growth. The source of external energy mayprovide thermal energy, for example, by resistively heating a wire coilin proximity to the growth sites (e.g., active growth material) or bypassing a current through a conductive growth substrate. In some cases,the source of external energy may provide an electric and/or magneticfield to the substrate. In some cases, the source of external energy maybe provided via magnetron heating, via laser, or via direct, resistiveheating the growth substrate, or a combination of one or more of these.The source of external energy may be provided as a component of a closedloop temperature control system in some embodiments. It may be providedas part of an open loop temperature control system in some embodiments.In an illustrative embodiment, the set of conditions may comprise thetemperature of the active growth material surface, the chemicalcomposition of the atmosphere surrounding the active growth material,the flow and pressure of reactant gas(es) (e.g., nanostructureprecursors) surrounding the active growth material surface and withinthe surrounding atmosphere, the deposition or removal of active growthmaterials or active growth material precursors, or other materials, onthe surface of the substrate (when present), and/or optionally the rateof motion of the substrate. In some cases, the source of external energymay provide X-rays to the growth substrate (when present) and/or activegrowth material. Not wishing to be bound by any particular theory, theX-rays might induce oxygen deficiency into the active growth material,might activate the active growth material, and/or it might change thegas species coming into contact with the active growth material.

According to certain embodiments, exposure of the precursor of thecarbon-based nanostructures to the active growth material may occur at aparticular temperature, pH, solvent, chemical reagent, type ofatmosphere (e.g., nitrogen, argon, oxygen, etc.), electromagneticradiation, or the like. In some cases, the set of conditions under whichthe precursor of the carbon-based nanostructures is exposed to theactive growth material may be selected to facilitate nucleation, growth,stabilization, removal, and/or other processing of nanostructures. Insome cases, the set of conditions may be selected to facilitatereactivation, removal, and/or replacement of the active growth material.In some cases, the set of conditions may be selected to maintain theactivity of the active growth material. Some embodiments may comprise aset of conditions comprising exposure to a source of external energy.The source of energy may comprise electromagnetic radiation, electricalenergy, sound energy, thermal energy, or chemical energy. For example,the set of conditions comprises exposure to heat or electromagneticradiation, resistive heating, exposure to a laser, or exposure toinfrared light. In some embodiments, the set of conditions comprisesexposure to a particular temperature, pressure, chemical species, and/ornanostructure precursor material.

According to certain embodiments, the growth of the carbon-basednanostructures from the precursors can occur under conditions which areselected such that carbon nanotubes are selectively produced. In manycases, conditions (e.g., temperature, pressure, etc.) that lead to theproduction of other carbon-based nanostructures, such as graphene,cannot be successfully used to produce nanotubes. In some cases, carbonnanotubes will not grow on traditional active growth materials fromwhich graphene will grow.

The growth of the carbon-based nanostructures can occur, in accordancewith certain embodiments, under a gaseous atmosphere. The atmosphere cancomprise the precursor and, optionally, one or more carrier gases whichare not consumed during carbon-based nanostructure growth. Examples ofsuitable carrier gases include, but are not limited to, helium, argon,and nitrogen.

In certain embodiments in which carbon dioxide and at least onehydrocarbon (e.g., at least one alkyne) are used in the precursor of thecarbon-based nanostructures, the molar ratio of carbon dioxide to thehydrocarbons (e.g., alkynes) is at least 0.01:1, at least 0.05:1, atleast 0.1:1; at least 0.2:1, at least 0.5:1, at least 1:1, or at least2:1 (and/or, in certain embodiments, up to 10:1, up to 13:1, up to 15:1,up to 20:1, up to 100:1, or more). In some embodiments in which carbondioxide and at least one hydrocarbon are used in the precursor of thecarbon-based nanostructures, the molar ratio of carbon dioxide to thehydrocarbons is at least 0:1, at least 0.01:1, at least 0.05:1, at least0.1:1; at least 0.2:1, at least 0.5:1, at least 1:1, or at least 2:1(and/or, in certain embodiments, up to 0.01:1, up to 0.05:1, up to0.1:1, up to 0.2:1, up to 0.5:1, up to 1:1, up to 2:1, up to 10:1, up to13:1, up to 15:1, up to 20:1, up to 100:1, or more). For example, insome embodiments in which carbon dioxide and acetylene (C₂H₂) are usedin the precursor of the carbon-based nanostructures, the molar ratio ofcarbon dioxide to acetylene is at least 0.01:1, at least 0.05:1, atleast 0.1:1; at least 0.2:1, at least 0.5:1, at least 1:1, or at least2:1 (and/or, in certain embodiments, up to 10:1, up to 13:1, up to 15:1,up to 20:1, up to 100:1, or more).

In some cases, exposure occurs at pressures comprising substantiallyatmospheric pressure (i.e., about 1 atm or 760 torr). In some cases,exposure occurs at a pressure of less than 1 atm (e.g., less than 100torr, less than 10 torr, less than 1 torr, less than 0.1 torr, less than0.01 torr, or lower). In some cases, the use of high pressure may beadvantageous. For example, in some embodiments, exposure to a set ofconditions comprises exposure at a pressure of at least 2 atm, at least5 atm, at least 10 atm, at least 25 atm, or at least 50 atm.

Introduction of gases to a gaseous atmosphere can occur at any suitablerate. In some embodiments, any gas present during the reaction may beintroduced to the gaseous atmosphere at a rate greater than or equal to5 sccm, greater than or equal to 10 sccm, greater than or equal to 25sccm, greater than or equal to 50 sccm, greater than or equal to 100sccm, greater than or equal to 150 sccm, greater than or equal to 500sccm, or greater than or equal to 1000 sccm. In some embodiments, anygas present during the reaction may be introduced to the gaseousatmosphere at a rate greater than or equal to 0.01 sccm, greater than orequal to 0.1 sccm, greater than or equal to 1 sccm, greater than orequal to 5 sccm, greater than or equal to 10 sccm, greater than or equalto 25 sccm, greater than or equal to 50 sccm, greater than or equal to100 sccm, greater than or equal to 150 sccm, greater than or equal to500 sccm, or greater than or equal to 1000 sccm. Any gas present duringthe reaction may be introduced to the gaseous atmosphere at a rate lessthan or equal to 1500 sccm, less than or equal to 1000 sccm, less thanor equal to 500 sccm, less than or equal to 150 sccm, less than or equalto 100 sccm, less than or equal to 50 sccm, less than or equal to 25sccm, or less than or equal to 10 sccm. Any gas present during thereaction may be introduced to the gaseous atmosphere at a rate less thanor equal to 1500 sccm, less than or equal to 1000 sccm, less than orequal to 500 sccm, less than or equal to 150 sccm, less than or equal to100 sccm, less than or equal to 50 sccm, less than or equal to 25 sccm,less than or equal to 10 sccm, less than or equal to 5 sccm, less thanor equal to 1 sccm, or less than or equal to 0.1 sccm. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 10 sccm and less than or equal to 25 sccm). Other ranges arealso possible. If more than one gas is introduced, the gases may beintroduced at the same rate or they may be introduced at differentrates. Gases may be introduced at the same time or at different times.The gases may be introduced in any order (e.g., the precursor may beintroduced prior to the introduction of any other gas, may be introducedafter all other gases have been introduced, or may be introduced beforesome gases but after others).

The carbon-based nanostructures may grow from the precursor at anysuitable rate. In some embodiments, the carbon-based nanostructures maygrow from the precursor such that lengths of carbon-based nanostructuresincrease at a rate of greater than or equal to 0.1 microns per minute,greater than or equal to 0.25 microns per minute, greater than or equalto 0.5 microns per minute, greater than or equal to 1 micron per minute,greater than or equal to 2.5 microns per minute, or greater than orequal to 5 microns per minute. In some embodiments, the carbon-basednanostructures may grow from the precursor such that lengths ofcarbon-based nanostructures increase at a rate of up to 10 microns perminute, up to 50 microns per minute, up to 100 microns per minute, ormore. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.1 microns per minute and up to 100microns per minute). Other ranges are also possible.

The carbon-based nanostructures may grow from the precursors for anyamount of time. In certain embodiments, the growth may occur over a timeperiod of greater than or equal to 1 minute, greater than or equal to 2minutes, greater than or equal to 5 minutes, greater than or equal to 10minutes, greater than or equal to 15 minutes, greater than or equal to30 minutes, or greater than or equal to 60 minutes. The growth may occurover a period of less than or equal to 90 minutes, less than or equal to60 minutes, less than or equal to 30 minutes, less than or equal to 15minutes, less than or equal to 10 minutes, less than or equal to 5minutes, or less than or equal to 2 minutes. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 5 minutes and less than or equal to 15 minutes). Other ranges arealso possible.

In certain embodiments, the active growth material, or a precursorthereof, is supported by a substrate. The substrate can be a singlematerial or it may be a composite substrate that includes more than onecomponent. A variety of growth substrates may be used in accordance withcertain of the systems and methods described herein. Growth substratesmay comprise any material capable of supporting the active growthmaterial, or a precursor thereof, and/or the carbon-based nanostructuresthat are grown. The growth substrate may be selected to be inert toand/or stable under sets of conditions used in a particular process,such as nanostructure growth conditions, nanostructure removalconditions, and the like. In some cases, the growth substrate comprisesa substantially flat surface. In some cases, the growth substratecomprises a substantially nonplanar surface. For example, the growthsubstrate may comprise a cylindrical surface.

In some embodiments, the substrate may be a solid. According to certainembodiments, the solid may be a single phase material such as a metal,ceramic, or polymer. The solid may be a composite, in some embodiments.In certain embodiments, the solid may be in any state of crystallinityincluding single crystalline, polycrystalline, semicrystalline, and/oramorphous.

According to certain embodiments, the substrate (or a component of acomposite substrate) can be sensitive to elevated temperatures. Forexample, in some embodiments, the substrate (or a component of acomposite substrate) can undergo a phase change or a substantial loss ofmass when heated to relatively low temperatures. One advantage ofcertain (although not necessarily all) embodiments is that carbon-basednanostructures can be grown at relatively low temperatures, which canallow for the growth of carbon-based nanostructures on substrates thatwere believed to be too temperature-sensitive to support carbon-basednanostructure growth without changing phase or degrading.

According to certain embodiments, the active growth material, or aprecursor thereof, is supported by a substrate that undergoes a phasechange or substantial loss of mass when at a temperature below 800° C.in a 100% nitrogen atmosphere. To determine whether a particularsubstrate undergoes a phase change or a substantial loss of mass when ata temperature below 800° C. in a 100% nitrogen atmosphere, one wouldheat the substrate within the 100% nitrogen atmosphere from 25° C. at aramp rate of 5° C./minute. If the substrate undergoes a phase change atany temperature below 800° C. under these conditions, then the substratewould be said to undergo a phase change at a temperature below 800° C.in a 100% nitrogen atmosphere. If the substrate undergoes a substantialloss of mass (i.e., a loss of mass of 0.1% or more, relative to theinitial mass, such as a loss of 0.5% or more, 1% or more, 2% or more, or5% or more) at any temperature below 800° C. under these conditions,then the substrate would be said to undergo a substantial loss of massat a temperature below 800° C. in a 100% nitrogen atmosphere. In someembodiments, the substrate can be a substrate that undergoes a phasechange or substantial loss of mass when at a temperature below 700° C.,below 650° C., below 600° C., below 550° C., below 500° C., below 475°C., below 450° C., or below 425° C. in a 100% nitrogen atmosphere. Otherranges are also possible. In certain embodiments, a composite substrateis employed, and the component of the composite substrate that contactscarbon-based nanostructures can be one that undergoes a phase change orsubstantial loss of mass when at a temperature below 800° C., below 700°C., below 650° C., below 600° C., below 550° C., below 500° C., below475° C., below 450° C., or below 425° C. in a 100% nitrogen atmosphere.

According to certain embodiments, the active growth material, or aprecursor thereof, is supported by a substrate that undergoes a phasechange or substantial change in mass when at a temperature below 650° C.in a 100% oxygen atmosphere. To determine whether a particular substrateundergoes a phase change or a substantial change in mass when at atemperature below 650° C. in a 100% oxygen atmosphere, one would heatthe substrate within the 100% oxygen atmosphere from 25° C. at a ramprate of 5° C./minute. If the substrate undergoes a phase change at anytemperature below 650° C. under these conditions, then the substratewould be said to undergo a phase change at a temperature below 650° C.in a 100% oxygen atmosphere. If the substrate undergoes a substantialchange in mass (i.e., a gain or loss of mass of 0.1% or more, relativeto the initial mass, such as a gain or less of mass of 0.5% or more, 1%or more, 2% or more, or 5% or more) at any temperature below 650° C.under these conditions, then the substrate would be said to undergo asubstantial change in mass at a temperature below 650° C. in a 100%oxygen atmosphere. In some embodiments, the substrate can be a substratethat undergoes a phase change or a substantial change in mass when at atemperature below 600° C., below 550° C., below 500° C., below 475° C.,below 450° C., or below 425° C. in a 100% oxygen atmosphere. Otherranges are also possible.

In certain embodiments, a composite substrate is employed, and thecomponent of the composite substrate that contacts carbon-basednanostructures can be one that undergoes a phase change or substantialchange in mass when at a temperature below 650° C., below 600° C., below550° C., below 500° C., below 475° C., below 450° C., or below 425° C.in a 100% oxygen atmosphere.

In some embodiments, the phase change that the substrate undergoes(e.g., within any of the temperature ranges outlined above) may comprisea glass transition, a transition between different crystal structures, amelting transition, a vaporization or condensation transition,sublimation, and/or the transition to a plasma. In some embodiments, thephase change that the substrate undergoes (e.g., within any of thetemperature ranges outlined above) comprises a glass transition. In someembodiments, the phase change that the substrate undergoes (e.g., withinany of the temperature ranges outlined above) comprises melting. Incertain embodiments, the phase change that the substrate undergoes(e.g., within any of the temperature ranges outlined above) comprisesvaporization and/or sublimation. One of ordinary skill in the art wouldbe aware of methods for measuring a phase transition. For example, phasetransitions can be assessed by differential scanning calorimetry,polarized light microscopy, rheology, visual observation, or othermethods.

In some embodiments, the substrate as a whole undergoes the substantialchange (e.g., increase or decrease) in mass and/or phase change underthe conditions described above. In certain embodiments, a component of acomposite substrate may undergo the substantial change (e.g., increaseor decrease) in mass and/or phase change under the conditions describedabove. For example, in some embodiments, a composite substratecomprising a fiber and a sizing layer may be used as a substrate. Insome such embodiments, the sizing layer of the composite substrate mayundergo a phase change and/or a substantial change in mass whenprocessed as outlined above (e.g., at at least one temperature below800° C. when in a nitrogen and/or oxygen atmosphere, as describedabove).

In accordance with certain embodiments, a substantial change in mass(e.g., of a substrate or a component of a composite substrate) is achange in mass (an increase or decrease) greater than or equal to 0.1%of the initial mass (e.g., when under a nitrogen and/or oxygenatmosphere, as described above). In some embodiments, the substantialchange in mass can be greater than or equal to 0.5%, 1%, 2%, 5%, 10%,20%, or 50% of the initial mass (e.g., when under a nitrogen and/oroxygen atmosphere, as described above). One of ordinary skill in the artwould also be aware of methods for measuring mass loss. For example,mass loss can be assessed by thermogravimetric analysis (under theappropriate atmosphere). In some embodiments, the substrate does notundergo a phase transition or substantial loss of mass (i.e., a loss ofmass of more than 0.1%) during the nanostructure growth process. In someembodiments, the substrate does not undergo a phase transition duringthe nanostructure growth process. In certain embodiments, the substratedoes not undergo a substantial loss of mass during the nanostructuregrowth process. In other embodiments, the substrate may undergo a phasetransition during the nanostructure growth process.

According to some embodiments, the substrate (e.g., on which the activegrowth material and/or the carbon based nanostructures are supported) isa polymeric substrate. Generally, polymers are materials comprisingthree or more repeating mer units in their chemical structure. Polymersmay comprise additional repeating units and may have any molecularweight. In some embodiments, the substrate may comprise polymers thatare in the form of fibers, or may comprise polymeric fibers.

In some embodiments, the polymer of the substrate has a number averagemolecular weight of greater than or equal to 1,000 Da, greater than orequal to 5,000 Da, greater than or equal to 10,000 Da, greater than orequal to 25,000 Da, greater than or equal to 50,000 Da, greater than orequal to 100,000 Da, or greater than or equal to 500,000 Da. The polymerin the substrate may have a number average molecular weight less than orequal to 1,000,000 Da, less than or equal to 500,000 Da, less than orequal to 100,000 Da, less than or equal to 50,000 Da, less than or equalto 25,000 Da, less than or equal to 10,000 Da, or less than or equal to5,000 Da. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 10,000 Da and less than or equal to50,000 Da). Other ranges are also possible.

In certain embodiments, the polymer of the substrate has a weightaverage molecular weight of greater than or equal to 1,000 Da, greaterthan or equal to 5,000 Da, greater than or equal to 10,000 Da, greaterthan or equal to 25,000 Da, greater than or equal to 50,000 Da, greaterthan or equal to 100,000 Da, or greater than or equal to 500,000 Da. Thepolymer in the substrate may have a weight average molecular weight lessthan or equal to 1,000,000 Da, less than or equal to 500,000 Da, lessthan or equal to 100,000 Da, less than or equal to 50,000 Da, less thanor equal to 25,000 Da, less than or equal to 10,000 Da, or less than orequal to 5,000 Da. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 10,000 Da and less than orequal to 50,000 Da). Other ranges are also possible.

The polymer in the substrate may have any chain structure in accordancewith certain embodiments. In some embodiments, polymers may be linear,branched, and/or crosslinked molecules. Or they may be in the form of acrosslinked network. Polymers may have branches or crosslinks of anymolecular weight, functionality, and/or spacing. In accordance with someembodiments, the polymers may be highly monodisperse. In accordance withother embodiments, the polymers may be polydisperse. One of ordinaryskill in the art would be aware of methods for dispersity. For example,dispersity can be assessed by size-exclusion chromatography.

Polymeric substrates may have any desired mechanical property. Incertain embodiments, polymeric substrates are rubbery, glassy, and/orsemicrystalline.

In some embodiments, the polymers can be homopolymers, blends ofpolymers, and/or copolymers. Copolymers may be random copolymers,tapered copolymers, and block copolymers. In certain embodiments, blockcopolymers with more than three blocks may comprise two or more blocksformed from the same monomer. Blends of polymers can be phase separatedor single phase, according to some embodiments.

In some embodiments, polymers may be organic polymers, inorganicpolymers, or organometallic polymers. It may be advantageous, accordingto certain but not necessarily all embodiments, for the substrate tocomprise an organic polymer material. In such embodiments, at least 50%,at least 75%, at least 90%, at least 95%, or at least 99%, or 100% ofthe polymeric substrate is made up of organic polymer material. Incertain embodiments, polymers are of synthetic origin. Polymers ofsynthetic origin may be formed by either step growth or chain growthprocesses, and may be further functionalized after polymerization.Non-limiting examples of suitable polymers include polystyrene,polyethylene, polypropylene, poly(methyl methacrylate),polyacrylonitrile, polybutadiene, polyisoprene, poly(dimethyl siloxane),poly(vinyl chloride), poly(tetrafluoroethylene), polychloroprene,poly(vinyl alcohol), poly(ethylene oxide), polycarbonate, polyester,polyamide, polyimide, polyurethane, poly(ethylene terephthalate),polymerized phenol-formaldehyde resin, polymerized epoxy resin,para-amid fibers, silk, collagen, keratin, and gelatin. Additionalexamples of suitable polymers that can be used in the growth substrateinclude, but are not limited to, relatively high temperaturefluoropolymers (e.g., Teflon®), polyetherether ketone (PEEK), andpolyether ketone (PEK). In some embodiments, the polymer is not apolyelectrolyte.

In some embodiments, polymeric substrates my further comprise additives.Polymeric substrates may be in the form of a gel and comprise solvent,according to certain embodiments. In some embodiments, polymericsubstrates may comprise one or more of fillers, additives, plasticizers,small molecules, and particles comprising ceramic and/or metal. Incertain embodiments, greater than or equal to 50%, greater than or equalto 80%, greater than or equal to 90%, greater than or equal to 95%, orgreater than or equal to 99% of the mass of the polymeric substrate maycomprise polymers. Other ranges are also possible.

According to certain embodiments, the polymer may form one component ofa composite substrate. For example, the polymer can be a coating formedover a fiber, such as a carbon fiber. As one non-limiting example, insome embodiments, the substrate comprises a sized carbon fiber.

In some embodiments, the substrate may comprise carbon (e.g., amorphouscarbon, carbon aerogel, carbon fiber, graphite, glassy carbon,carbon-carbon composite, graphene, aggregated diamond nanorods,nanodiamond, diamond, and the like).

In accordance with certain embodiments, the substrate (e.g., on whichthe active growth material, or a precursor thereof, and/or thecarbon-based nanostructures are supported) comprises a fiber. Forexample, in some embodiments, the active growth material, active growthmaterial precursor, and/or carbon-based nanostructures are supported ona carbon fiber. In certain embodiments, the active growth material,active growth material precursor, and/or carbon-based nanostructures aresupported on a glass fiber. In accordance with some embodiments, theactive growth material, active growth material precursor, and/orcarbon-based nanostructures are supported on fibers comprising one ormore of the following materials: carbon; carbon glass; glass; alumina;basalt; metals (e.g., steel, aluminum, titanium); aramid (e.g., Kevlar®,meta-aramids such as Nomex®, p-aramids); liquid crystalline polyester;poly(p-phenylene-2,6-benzobisoxazole) (PBO); polyethylene (e.g.,Spectra®); poly{2,6-diimidazo[4,5-b:4′,5′-e]pyridinylene-1,4-(2,5-dihydroxy)phenylene};and combinations of these. In some embodiments, the active growthmaterial, active growth material precursor, and/or carbon-basednanostructures are supported on fibers comprising at least one ofpolyetherether ketone (PEEK) and polyether ketone (PEK). For example, inFIG. 1C, substrate 308 is an elongated substrate, and can correspond to,for example, a fiber such as a carbon fiber. Substrate 308 can be indirect contact with active growth material 106. In some suchembodiments, carbon-based nanostructures 102 can be grown from precursor104 on active growth material 106.

As noted above, in some embodiments, the active growth material, activegrowth material precursor, and/or carbon based nanostructures aresupported on a carbon fiber (e.g., a sized carbon fiber or an unsizedcarbon fiber). Any suitable type of carbon fiber can be employedincluding, for example, aerospace-grade carbon fibers, auto/sport gradecarbon fibers, and/or microstructure carbon fibers. In certainembodiments, intermediate modulus (IM) or high modulus (HM) carbonfibers can be employed. In some embodiments, poly(acrylonitrile)-derivedcarbon fibers can be employed. Certain embodiments of the invention areadvantageous for use with carbon fibers that carry a large degree oftheir tensile strengths in their outer skins (e.g., fibers in which atleast 50%, at least 75%, or at least 90% of the tensile strength isimparted by the portion of the fiber located a distance away from theouter skin of the fiber of less than 0.1 times or less than 0.05 timesthe cross-sectional diameter of the fiber), such as aerospace gradeintermediate modulus carbon fibers.

In certain embodiments, the substrate can be a carbon-based substrate.In some embodiments, the carbon-based growth substrate contains carbonin an amount of at least 75 wt %, at least 90 wt %, at least 95 wt %, orat least 99 wt %. That is to say, in some embodiments, at least 75 wt %,at least 90 wt %, at least 95 wt %, or at least 99 wt % of thecarbon-based growth substrate is made of carbon.

In some embodiments, the growth substrate can be elongated. For example,the ratio of the length of the growth substrate (e.g., a fibersubstrate) to the diameter or other cross-sectional dimension of thegrowth substrate can be, in some embodiments, at least 2:1; at least3:1; at least 5:1; at least 10:1; at least 50:1; at least 100:1; atleast 500:1; at least 1000:1; at least 10,000:1; at least 100,000:1; atleast 10⁶:1; at least 10⁷:1; at least 10⁸:1; or at least 10⁹:1.

In certain embodiments, fibers (e.g., carbon fibers) used as growthsubstrates can have relatively large cross-sectional dimensions (e.g.,relative to the nanostructures grown over the fiber substrate). Forexample, in certain embodiments, a fiber growth substrate can have asmallest cross-sectional dimension of at least 1 micrometer, at least 5micrometers, or at least 10 micrometers (and/or, in certain embodiments,less than 1 mm, less than 100 micrometers, or less than 20 micrometers).Generally, the smallest cross-sectional dimension is measuredperpendicularly to the length of the fiber and through the longitudinalaxis of the fiber.

In certain embodiments, the active growth material, active growthmaterial precursor, and/or carbon-based nanostructures are supported ona sized carbon fiber. The sized carbon fiber can be a single carbonfiber or part of a collection of a plurality of fibers. The collectionof fibers may be, according to certain embodiments, a unidirectionalcollection, a tow, or a weave. Those of ordinary skill in the art arefamiliar with “sized” fibers (including “sized” carbon fibers). Sizedfibers generally include a coating material (e.g., a polymer or othercoating material) that protects the underlying fiber material (e.g.,carbon) from oxygen and/or other chemicals in the surroundingenvironment. According to certain embodiments, the sized fiber compriseone or more polymers within the sizing layer. Non-limiting examples ofpolymers that may be included in the sizing of a sized fiber (e.g., asized carbon fiber) are organosilanes, epoxies, urethanes, polyesters,oligomer polyimides, phenylethynyl-terminated imide oligomers, oligomerpolyamides, polyhydroxyethers, nylons, and combinations of these. Insome embodiments, the polymer of the sizing material is not apolyelectrolyte.

For example, in FIG. 1D, substrate 308 can be a fiber, such as a carbonfiber. Material 408 can be a polymeric material, such as sizing that isapplied to sized fibers (e.g., sized carbon fibers). In some suchembodiments, active growth material 106 can be applied to material 408.In some embodiments, carbon-based nanostructures 102 can be grown onactive growth material 106 (as well as on material 408 and substrate308) from nanostructure precursor 104. According to certain embodiments,the carbon-based nanostructures can be grown without causing material408 to lose a substantial amount of mass (i.e., a loss of mass of 0.1%or more, or, in some cases, any of the other ranges described elsewhereherein) and/or without causing material 408 to undergo a phase change.

In certain embodiments, the active growth material, active growthmaterial precursor, and/or carbon-based nanostructures are supported ona prepreg. As used herein, the term “prepreg” refers to one or morelayers of thermoset or thermoplastic resin containing embedded fibers,for example fibers of carbon, glass, silicon carbide, and the like. Insome embodiments, the thermoset material includes epoxy, rubberstrengthened epoxy, BMI, PMK-15, polyesters, and/or vinylesters. Incertain embodiments, the thermoplastic material includes polyamides,polyimides, polyarylene sulfide, polyetherimide, polyesterimides,polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfide,polyetherimide, polypropylene, polyolefins, polyketones,polyetherketones, polyetherketoneketone, polyetheretherketones, and/orpolyester. According to certain embodiments, the prepreg includes fibersthat are aligned and/or interlaced (woven or braided). In someembodiments, the prepregs are arranged such the fibers of many layersare not aligned with fibers of other layers, the arrangement beingdictated by directional stiffness requirements of the article to beformed. In certain embodiments, the fibers cannot be stretchedappreciably longitudinally, and thus, each layer cannot be stretchedappreciably in the direction along which its fibers are arranged.Exemplary prepregs include TORLON thermoplastic laminate, PEEK(polyether etherketone, Imperial Chemical Industries, PLC, England),PEKK (polyetherketone ketone, DuPont) thermoplastic, T800H/3900 2thermoset from Toray (Japan), and AS4/3501 6 thermoset from Hercules(Magna, Utah).

In some embodiments in which substrates are employed, the active growthmaterial (or precursor thereof), the growth substrate, and/or theconditions under which the nanostructures are grown are selected suchthat the amount of chemical interaction or degradation between thesubstrate and the active growth material is relatively small. Forexample, in some cases, the active growth material does not diffusesignificantly into or significantly chemically react with the substrateduring formation of the nanostructures. One of ordinary skill in the artwill be able to determine whether a given active growth material hasdiffused significantly into or significantly chemically reacted with asubstrate. For example, X-ray photoelectron spectroscopy (XPS),optionally with depth profiling, may be used to determine whether anactive growth material has diffused into a substrate or whether elementsof the substrate have diffused into the active growth material. X-raydiffraction (XRD), optionally coupled with XPS, may be used to determinewhether an active growth material and a substrate have chemicallyreacted with each other. Secondary ion mass spectroscopy (SIMS) can beused to determine chemical composition as a function of depth.

FIG. 2 illustrates a set of embodiments in which active growth materialor active growth material precursor 106 can interact with substrate 108.The volume within which the active growth material or active growthmaterial precursor interacts with the substrate is shown as volume 118.In FIG. 2, spherical active growth material or active growth materialprecursor 106A interacts with substrate 108 over volume 118A, which isroughly equivalent to the original volume of active growth material oractive growth material precursor 102 A. Spherical active growth materialor active growth material precursor 106B interacts with substrate 108over volume 118B, which is roughly equivalent to three times theoriginal volume of active growth material or active growth materialprecursor 102B. Wetted active growth material or active growth materialprecursor 106C is shown interacting with substrate 108 over volume 118C,which is roughly equivalent to the original volume of active growthmaterial or active growth material precursor 106C. In addition,substrate 108 is illustrated diffusing into active growth material oractive growth material precursor 106D, with the interaction volumeindicated as volume 118D. In some embodiments, chemical reaction betweenthe active growth material or active growth material precursor and thesubstrate may occur, in which case the volume within which the activegrowth material or active growth material precursor and the substrateinteract is defined by the volume of the reaction product. The volume ofthe chemical product may be determined, for example, via XPS analysis,using XRD to determine the chemical composition of the product andverify that it originated from the active growth material or activegrowth material precursor. In some embodiments, the active growthmaterial or active growth material precursor may diffuse into thesubstrate or the substrate may diffuse into the active growth materialor active growth material precursor, in which case the volume withinwhich the active growth material or active growth material precursor andthe substrate interact is defined by the volume over which the activegrowth material, active growth material precursor, and/or the substratediffuses. The volume over which an active growth material or activegrowth material precursor diffuses can be determined, for example, usingXPS with depth profiling.

In some embodiments, the volume within which the active growth materialinteracts with the substrate (e.g., the volume of the product producedvia a chemical reaction between the active growth material and thesubstrate, the volume over which the active growth material and/orsubstrate diffuses into the other, etc.) is relatively small compared tothe original volume of the active growth material as formed on thesubstrate. In some instances, the volume of the active growth materialas formed on the substrate is at least 0.1%, at least 0.5%, at least 1%,at least 5%, at least 10%, at least 25%, at least 50%, at least 100%, atleast 200%, at least 500%, at least 2500%, at least 5000%, at least10,000%, at least 50,000%, or at least 100,000% greater than the volumewithin which the active growth material interacts with the substrate(e.g., via reaction, via diffusion, via a combination of mechanisms,etc.).

In some embodiments, the mass percentage of the active growth materialthat interacts with the substrate (e.g., via reaction of the activegrowth material and the substrate, diffusion of the active growthmaterial into substrate, diffusion of the substrate into the activegrowth material, or a combination of these) is relatively low. In someembodiments, less than 50 atomic %, less than 25 atomic %, less than 10atomic %, less than 5 atomic %, less than 2 atomic %, or less than 1atomic % of the active growth material as formed on the substrateinteracts with the substrate. The percentage of the active growthmaterial that interacts with the substrate can be determined, forexample, using XPS with depth profiling. Optionally, XRD can be employedto determine the composition of the measured material.

In some cases, the electrical resistance of the substrate does notchange, from the beginning to the end of the nanostructure growthprocess, by more than 100%, by more than 50%, by more than 25%, by morethan 10%, by more than 5%, or by more than 1% relative to the electricalresistance of a substrate exposed to essentially identical conditions inthe absence of the active growth material. In some embodiments, theelectrical resistance of the substrate does not decrease, from thebeginning to the end of the nanostructure growth process, by more than50%, by more than 25%, by more than 10%, by more than 5%, or by morethan 1% relative to the electrical resistance of a substrate exposed toessentially identical conditions in the absence of the active growthmaterial.

In some cases, the nanostructures may be removed from a substrate afterthe nanostructures are formed. For example, the act of removing maycomprise transferring the nanostructures directly from the surface ofthe substrate to a surface of a receiving substrate. The receivingsubstrate may be, for example, a polymer material or a carbon fibermaterial. In some cases, the receiving substrate comprises a polymermaterial, metal, or a fiber comprising Al₂O₃, SiO₂, carbon, or a polymermaterial. In some cases, the receiving substrate comprises a fibercomprising Al₂O₃, SiO₂, carbon, or a polymer material. In someembodiments, the receiving substrate is a fiber weave.

Removal of the nanostructures may comprise application of a mechanicaltool, mechanical or ultrasonic vibration, a chemical reagent, heat, orother sources of external energy, to the nanostructures and/or thesurface of the growth substrate. In some cases, the nanostructures maybe removed by application of compressed gas, for example. In some cases,the nanostructures may be removed (e.g., detached) and collected inbulk, without attaching the nanostructures to a receiving substrate, andthe nanostructures may remain in their original or “as-grown”orientation and conformation (e.g., in an aligned “forest”) followingremoval from the growth substrate. Systems and methods for removingnanostructures from a substrate, or for transferring nanostructures froma first substrate to a second substrate, are described in InternationalPatent Application Serial No. PCT/US2007/011914, filed May 18, 2007,entitled “Continuous Process for the Production of NanostructuresIncluding Nanotubes,” which is incorporated herein by reference in itsentirety.

In some embodiments, the active growth material may be removed from thegrowth substrate and/or the nanostructures after the nanostructures aregrown. Active growth material removal may be performed mechanically, forexample, via treatment with a mechanical tool to scrape or grind theactive growth material from a surface (e.g., of a substrate). In somecases, the first active growth material may be removed by treatment witha chemical species (e.g., chemical etching) or thermally (e.g., heatingto a temperature which evaporates the active growth material). Forexample, in some embodiments, the active growth material may be removedvia an acid etch (e.g., HCl, HF, etc.), which may, for example,selectively dissolve the active growth material. For example, HF can beused to selectively dissolve oxides. In some embodiments, the firstactive growth material may be removed by a combination of treatment witha chemical species and treatment with heat (e.g., the first activegrowth material may be heated in the presence of H₂). When heating isemployed to remove the first active growth material, it may be appliedby exposing the active growth material to a heated environment and/or byusing an electron beam to heat the active growth material.

While growth of nanostructures using a growth substrate has beenprimarily described above in detail, the embodiments described hereinare not so limited, and carbon-based nanostructures may be grown, insome embodiments, on an active growth material in the absence of agrowth substrate. For example, FIG. 1B includes a schematic illustrationof system 200 in which active growth material 106 is placed under a setof conditions selected to facilitate nanostructure growth in the absenceof a substrate in contact with the active growth material.Nanostructures 102 may grow from active growth material 106 as theactive growth material is exposed to the growth conditions. In someembodiments, the active growth material, or a precursor thereof, may besuspended in a fluid. For example, an active growth material, or aprecursor thereof, may be suspended in a gas (e.g., aerosolized) andsubsequently exposed to a carbon-containing precursor material, fromwhich carbon nanotubes may be grown. In some cases, the active growthmaterial, or a precursor thereof, may be suspended in a liquid (e.g., analcohol that serves as a nanostructure precursor material) during theformation of the nanostructures. In some embodiments, unsupported activegrowth materials, or precursors thereof, are in contact with a gas orvacuum at every point comprising their surfaces. It should be noted thatalthough the active growth material is depicted as a hemisphere in FIG.1B, active growth materials with other shapes are also contemplated,such as active growth materials with spherical shapes, polygonal shapes,and the like.

As noted above, certain embodiments are related to systems and methodsfor growing carbon-based nanostructures. As used herein, the term“carbon-based nanostructure” refers to articles having a fused networkof aromatic rings, at least one cross-sectional dimension of less than 1micron, and comprising at least 30% carbon by mass. In some embodiments,the carbon-based nanostructures may comprise at least 40%, at least 50%,at least 60%, at least 70%, at least 80%, at least 90%, or at least 95%of carbon by mass, or more. The term “fused network” would not include,for example, a biphenyl group, wherein two phenyl rings are joined by asingle bond and are not fused. Examples of carbon-based nanostructuresinclude carbon nanotubes (e.g., single-walled carbon nanotubes,double-walled carbon nanotubes, multi-walled carbon nanotubes, etc.),carbon nanowires, carbon nanofibers, carbon nanoshells, graphene,fullerenes, and the like. In some embodiments, the carbon-basednanostructures comprise hollow carbon nanoshells and/or nanohorns.

In some embodiments, a carbon-based nanostructure may have a least onecross-sectional dimension of less than 500 nm, less than 250 nm, lessthan 100 nm, less than 75 nm, less than 50 nm, less than 25 nm, lessthan 10 nm, or, in some cases, less than 1 nm. Carbon-basednanostructures described herein may have, in some cases, a maximumcross-sectional dimension of less than 1 micron, less than 500 nm, lessthan 250 nm, less than 100 nm, less than 75 nm, less than 50 nm, lessthan 25 nm, less than 10 nm, or, in some cases, less than 1 nm.

According to certain embodiments, the carbon-based nanostructures areelongated carbon-based nanostructures. As used herein, the term“elongated carbon-based nanostructure” refers to a carbon basednanostructure structure having an aspect ratio greater than or equal to10. In some embodiments, the elongated nanostructure can have an aspectratio greater than or equal to 100, greater than or equal to 1000,greater than or equal to 10,000, or greater. Those skilled in the artwould understand that the aspect ratio of a given structure is measuredalong the longitudinal axis of the elongated nanostructure, and isexpressed as the ratio of the length of the longitudinal axis of thenanostructure to the maximum cross-sectional diameter of thenanostructure.

In some embodiments, the carbon-based nanostructures described hereinmay comprise carbon nanotubes. As used herein, the term “carbonnanotube” is given its ordinary meaning in the art and refers to asubstantially cylindrical molecule or nanostructure comprising a fusednetwork of primarily six-membered rings (e.g., six-membered aromaticrings) comprising primarily carbon atoms. In some cases, carbonnanotubes may resemble a sheet of graphite formed into a seamlesscylindrical structure. In some cases, carbon nanotubes may include awall that comprises fine-grained sp² sheets. In certain embodiments,carbon nanotubes may have turbostratic walls. It should be understoodthat the carbon nanotube may also comprise rings or lattice structuresother than six-membered rings. Typically, at least one end of the carbonnanotube may be capped, i.e., with a curved or nonplanar aromaticstructure. Carbon nanotubes may have a diameter of the order ofnanometers and a length on the order of millimeters, or, on the order oftenths of microns, resulting in an aspect ratio greater than 100, 1000,10,000, 100,000, 10⁶, 10⁷, 10⁸, 10⁹, or greater. Examples of carbonnanotubes include single-walled carbon nanotubes (SWNTs), double-walledcarbon nanotubes (DWNTs), multi-walled carbon nanotubes (MWNTs) (e.g.,concentric carbon nanotubes), inorganic derivatives thereof, organicderivatives thereof, and the like. In some embodiments, the carbonnanotube is a single-walled carbon nanotube. In some cases, the carbonnanotube is a multi-walled carbon nanotube (e.g., a double-walled carbonnanotube). In some cases, the carbon nanotube comprises a multi-walledor single-walled carbon nanotube with an inner diameter wider than isattainable from a traditional catalyst or other active growth material.In some cases, the carbon nanotube may have a diameter less than 1micron, less than 500 nm, less than 250 nm, less than 100 nm, less than50 nm, less than 25 nm, less than 10 nm, or, in some cases, less than 1nm.

In certain embodiments, the elongated carbon-based nanostructures grownaccording to certain embodiments may have a relatively low tortuosity.Without wishing to be bound by any particular theory, it is believedthat the use of certain active growth materials described herein(optionally, in combination with low temperature growth, and optionallyusing carbon dioxide and/or alkyne carbon-based nanostructureprecursors) can lead to the production of elongated carbon-basednanostructures that are particularly straight, according to certainalthough not necessarily all embodiments. The tortuosity (or r) may bedefined as the ratio of true length of the carbon-based nanostructure(L_(cnt)) to the length of the line segment connecting one end of thecarbon-based nanostructure to the other end of the carbon-basednanostructure (H); or, τ=L_(cnt)/H. In some embodiments, the elongatedcarbon-based nanostructures may have a tortuosity of less than or equalto 5, less than or equal to 4, less than or equal to 3, less than orequal to 2.5, less than or equal to 2.4, less than or equal to 2.3, lessthan or equal to 2.2, less than or equal to 2.1, less than or equal to2, less than or equal to 1.9, less than or equal to 1.8, less than orequal to 1.7, less than or equal to 1.6, less than or equal to 1.5, lessthan or equal to 1.4, less than or equal to 1.3, less than or equal to1.2, or less than or equal to 1.1. Other ranges are also possible. Forexample, FIG. 3A shows a highly tortuous carbon-based nanostructure 102attached to active growth material 106; FIG. 3B shows a moderatelytortuous nanostructure 102 attached to active growth material 106; andFIG. 3C shows a perfectly straight nanostructure 102 attached to activegrowth material 106 with a tortuosity of exactly 1. In FIGS. 3A, 3B, and3C, L_(cnt) is indicated by 502 and H is indicated by 504.

In some embodiments, the systems and methods described herein may beused to produce substantially aligned nanostructures. The substantiallyaligned nanostructures may have sufficient length and/or diameter toenhance the properties of a material when arranged on or within thematerial. In some embodiments, the set of substantially alignednanostructures may be formed on a surface of a substrate, and thenanostructures may be oriented such that the long axes of thenanostructures are substantially non-planar with respect to the surfaceof the substrate. In some cases, the long axes of the nanostructures areoriented in a substantially perpendicular direction with respect to thesurface of the substrate, forming a nanostructure array or “forest.” Theforest may comprise, according to some embodiments, at least 100nanostructures, at least 1000 nanostructures, at least 10⁴nanostructures, at least 10⁵ nanostructures, at least 10⁶nanostructures, at least 10⁷ nanostructures, at least 10⁸nanostructures, or more, for example, arranged in a side-by-sideconfiguration. The alignment of nanostructures in the nanostructure“forest” may be substantially maintained, even upon subsequentprocessing (e.g., transfer to other surfaces and/or combining theforests with secondary materials such as polymers), in some embodiments.Systems and methods for producing aligned nanostructures and articlescomprising aligned nanostructures are described, for example, inInternational Patent Application Serial No. PCT/US2007/011914, filed May18, 2007, entitled “Continuous Process for the Production ofNanostructures Including Nanotubes”; and U.S. Pat. No. 7,537,825, issuedon May 26, 2009, entitled “Nano-Engineered Material Architectures:Ultra-Tough Hybrid Nanocomposite System,” which are incorporated hereinby reference in their entirety.

Certain aspects are related to articles comprising substrates, polymericmaterial, and carbon-based nanostructures. As noted above, one advantageassociated with certain, but not necessarily all, embodiments describedherein is that carbon-based nanostructures can be grown on materialsthat would otherwise be incompatible with carbon-based nanostructuregrowth. For example, according to certain embodiments, the ability togrow carbon-based nanostructures at relatively low temperatures canallow one to grow carbon-based nanostructures on polymeric materialsand/or other temperature-sensitive materials without substantiallyaltering and/or damaging the temperature-sensitive materials.

In one set of embodiments, the inventive article comprises a substrate,a polymeric material at least partially coating the substrate,carbon-based nanostructures supported by the substrate, and an activegrowth material associated with the carbon-based nanostructures. Oneexample of such an arrangement is illustrated, for example, in FIG. 1D.In FIG. 1D, material 408 (which can be a polymeric material) at leastpartially coats substrate 308. While substrate 308 is illustrated inFIG. 1D as being cylindrical, the substrate could have a variety ofother suitable geometries. In FIG. 1D, active growth material 106 issupported by material 408 and substrate 308. In addition, carbon-basednanostructures 102 are illustrated as being supported by material 408and substrate 308.

In some embodiments, the active growth material can be between thecarbon-based nanostructures and the polymeric material. For example,referring to FIG. 1D, active growth material 106 is located betweencarbon-based nanostructures 102 and material 408. In some embodiments,the carbon-based nanostructures can be between the active growthmaterial and the polymeric material. The carbon-based nanostructures andthe active growth material can be in direct contact, according tocertain embodiments.

The active growth material can be any of the active growth materialsdescribed above or elsewhere herein, including active growth materialscomprising at least one of an alkali metal and an alkaline earth metal.The active growth material can also have any of the forms describedabove or elsewhere herein.

The substrate of the article can be any of the substrates describedelsewhere herein. In some embodiments, the substrate can be relativelytemperature sensitive. For example, as described above, in someembodiments, the substrate (or a component of a composite substrate)undergoes a phase change or a substantial loss of mass at a temperaturebelow 800° C. (or within any of the other temperature ranges describedabove or elsewhere herein) in a 100% nitrogen atmosphere. In certainembodiments, as described above, the substrate (or a component of acomposite substrate) undergoes a phase change or a substantial change inmass at a temperature below 650° C. (or within any of the othertemperature ranges described above or elsewhere herein) in a 100% oxygenatmosphere. In some embodiments, the substrate is an elongatedsubstrate. For example, in some embodiments, the substrate comprises afiber, such as a carbon fiber. In some embodiments, the substrate is asized carbon fiber. For example, referring to FIG. 1D, substrate 308 canbe a carbon fiber and material 408 can be a sizing material that atleast partially coats the carbon fiber. Examples of materials from whichthe sizing can be made are described, for example, above with respect tosized fibers.

In some embodiments, the polymeric material covers a relatively largepercentage of the external surface of the substrate. For example, insome embodiments, the polymeric material covers at least 50%, at least75%, at least 90%, at least 95%, at least 99%, or all of the externalsurface of the substrate. Referring to FIG. 1D, for example, material408 covers 100% of the external surface of the substrate 308.

According to certain embodiments, the thickness of the polymericmaterial can be relatively consistent over the underlying substrate. Forexample, in certain embodiments, the thickness of the polymericmaterial, over at least 80% of the surface area of the substrate that iscovered by the polymeric material, does not deviate from the averagethickness of the polymeric material by more than 50%, more than 40%,more than 30%, more than 20%, more than 10%, or more than 5%. In someembodiments, the thickness of the polymeric material, over at least 90%(or at least 95%, at least 98%, or at least 99%) of the surface area ofthe substrate that is covered by the polymeric material, does notdeviate from the average thickness of the polymeric material by morethan 50%, more than 40%, more than 30%, more than 20%, more than 10%, ormore than 5%. Such uniformity's may be observed, for example, in thesizing layer of certain sized fibers, such as certain sized carbonfibers.

The average thickness of the polymeric material can be, according tocertain embodiments, relatively thin. For example, according to certainembodiments, the average thickness of the polymeric material can be lessthan 1 micron, less than 500 nm, less than 200 nm, less than 100 nm,less than 50 nm, or less than 10 nm (and/or, in certain embodiments, aslittle as 1 nm, as little as 0.1 mm, or less).

The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

Example 1

In this example, desized carbon fibers are prepared for carbon-basednanostructure growth. Desized Tohotenax HTA40 fibers were rinsed oncewith water and then dried (under vacuum at 50 mbar and 120° C. for 20minutes). FIG. 4 is an SEM image of the as-received desized TohotenaxHTA40 fibers.

Comparative Example 2

This example shows the lack of growth of carbon-based nanostructuresfrom iron-comprising active growth materials at low growth temperatures.Desized carbon fibers (CF) were prepared as in Example 1. 0.05M ironnitrate in isopropanol was prepared and stirred for 60 minutes beforebeing poured into a petri dish. Desized CF were immersed in the 0.05Miron nitrate solution for 5 minutes, and then picked up and allowed todry at ambient temperatures for 3 hours.

A growth process was then performed as follows. The CF sample wasinserted into the center of a quartz tube housed within a Lindberg/BlueM Minimite furnace. The iron nitrate was in solid salt form on the CFsample just prior to commencing the growth process. The tube was firstflushed with argon for 2 minutes at 750 sccm at room temperature. Thegas flow was then switched to 400 sccm of hydrogen, and 100 sccm ofargon as the temperature ramped to 480° C. Once the temperature wasreached, both hydrogen and argon were shut off, and 16.7 sccm of CO₂ and167 sccm of a mixture of 10% acetylene and 90% argon was flowed throughthe tube for 15 minutes. Afterwards, all gases and heaters were shutoff, and argon was turned back on at 750 sccm while the furnace cooledback to room temperature. FIG. 5 is an SEM image of the desized CFsubstrate after the conclusion of the above procedure showing nocarbon-based nanostructure growth.

Example 3

In this example, growth of carbon nanotubes from a sodium hydroxide(NaOH) active growth material supported by desized CF is demonstrated.Desized CF were prepared as in Example 1. A 0.18 M solution of NaOH(Sigma Aldrich reagent grade) was prepared in deionized water, and addedto a petri dish. The desized CF were immersed in the 0.18M NaOH solutionfor 5 minutes, and then picked up and allowed to dry at ambienttemperature for 3 hours.

A growth process was performed as in Comparative Example 2. The sodiumhydroxide was in solid salt form on the CF sample just prior tocommencing the growth process. FIGS. 6A and 6B are SEM images showingcarbon nanotube growth at the conclusion of the growth process. FIG. 6Cis a TEM image of a carbon nanotube that was produced during the growthprocess. Carbon nanotube growth was also observed at 400° C. and at 390°C.

Example 4

This example shows growth of carbon nanotubes from a NaOH active growthmaterial supported by sized CF. Hexcel AS4 sized CF were rinsed anddried as in Example 1. A 0.18 M solution of NaOH (Sigma Aldrich reagentgrade) was prepared in deionized water, and added to a petri dish. Thesized CF were immersed in the 0.18M NaOH solution for 5 minutes, andthen picked up and allowed to dry at ambient temperature for 3 hours.

A growth process was performed as in Comparative Example 2. The sodiumhydroxide was in solid salt form on the CF sample just prior tocommencing the growth process. FIG. 7 is an SEM image showing carbonnanotubes that were produced during the growth process. Carbon nanotubegrowth was also observed at 400° C.

Example 5

In this example, growth of carbon nanotubes from a sodium carbonate(Na₂CO₃) active growth material supported by a desized CF substrate isshown. The desized CF substrate was a Tohotenax HTA40 fiber. Desized CFwere prepared as in Example 1. A 0.09 M solution of Na₂CO₃ (VWR reagentgrade) was prepared in deionized water, and added to a petri dish. Thedesized CF were immersed in the 0.09M Na₂CO₃ solution for 5 minutes, andthen picked up and allowed to dry at ambient temperatures for 3 hours.

A growth process was performed as in Comparative Example 2. The sodiumcarbonate was in solid salt form on the CF sample just prior tocommencing the growth process. FIG. 8 is an SEM image showing carbonnanotubes that were produced during the growth process.

Example 6

In this example, growth of carbon nanotubes from a sodium bicarbonate(NaHCO₃) active growth material supported by a desized CF substrate isdemonstrated. The desized CF substrate was a Tohotenax HTA40 fiber.Desized CF were prepared as in Example 1. A 0.18 M solution ofNaHCO₃(VWR reagent grade) was prepared in deionized water, and added toa petri dish. The desized CF were immersed in the 0.18M NaHCO₃ solutionfor 5 minutes, and then picked up and allowed to dry at ambienttemperatures for 3 hours.

A growth process was performed as in Comparative Example 2. The sodiumbicarbonate was in solid salt form on the CF sample just prior tocommencing the growth process. FIG. 9 is an SEM image showing carbonnanotubes that were produced during the growth process.

Example 7

This example demonstrates the growth of carbon nanotubes from a NaOHactive growth material supported by an alumina fiber substrate. Aluminafibers (Cotronics Corporation ULTRA TEMP 391) were used, as received, asa substrate. 0.18 M solution of NaOH (Sigma Aldrich reagent grade) wasprepared in deionized water, and added to a petri dish. The aluminafibers were immersed in the 0.18M NaOH solution for 5 minutes, and thenpicked up and allowed to dry at ambient temperatures for 3 hours.

A growth process was performed as in Comparative Example 2. The sodiumhydroxide was in solid salt form on the alumina fiber substrate justprior to commencing the growth process. FIG. 10 is an SEM image showingcarbon nanotubes that were produced during the growth process. Carbonnanotube growth was also observed at 400° C.

Example 8

This example shows carbon-based nanostructure growth from a NaOH activegrowth material supported by a polyelectrolyte substrate. The substratewas prepared by dissolving 1.4 g of poly(styrene-alt-maleic acid) (PSMA)(Sigma Aldrich reagent grade) in 25 mL of acetone and mixing thissolution with 0.18M of NaOH (prepared as in Example 3). This PSMA andNaOH solution was dropcast onto glass plates (VWR microscope slides).

A growth process was performed as in Comparative Example 2. The sodiumhydroxide was in solid salt form on the substrate just prior tocommencing the growth process. FIGS. 11A-F are SEM images showing carbonnanotubes that were produced during the growth process. Carbon nanotubegrowth was also observed at 400° C.

Example 9

In this example, carbon-based nanostructure growth from a potassiumcarbonate (K₂CO₃) active growth material supported by a polyelectrolytesubstrate is demonstrated. The substrate was prepared by dissolving 1.4g of PSMA in 25 mL of acetone and mixing this solution with 0.038 M ofK₂CO₃ in water. This PSMA and K₂CO₃ solution was dropcast onto glassplates (VWR microscope slides) and allowed to dry at room pressure andtemperature.

A growth process was performed as in Comparative Example 2. Thepotassium carbonate was in solid salt form on the substrate just priorto commencing the growth process. FIGS. 12A-F are SEM images showingcarbon nanotubes that were produced during the growth process. Carbonnanotube growth was also observed at 400° C.

Example 10

In this example, carbon-based nanostructure growth from a Na₂CO₃ activegrowth material supported by a titanium substrate is shown. Titaniumsheets (McMaster-Carr 9051K67 Grade 2) were sanded with 500 gritsandpaper, rinsed with deionized water, and dried under ambientconditions. A 0.18M Na₂CO₃ in water solution was drop-cast onto thetitanium sheets and allowed to dry at room pressure and temperature.

A growth process was performed as in Comparative Example 2. The Na₂CO₃was in solid salt form on the substrate just prior to commencing thegrowth process. FIGS. 13A-E are SEM images showing carbon nanotubes thatwere produced during the growth process. Carbon nanotube growth was alsoobserved at 400° C.

Example 11

This example shows carbon-based nanostructure growth from a NaHCO₃active growth material supported by a titanium substrate. Titaniumsheets (McMaster-Carr 9051K67 Grade 2) were sanded with 500 gritsandpaper, rinsed with deionized water, and dried under ambientconditions. A 0.18M NaHCO₃ in water solution was drop-cast onto thetitanium sheets and allowed to dry at room pressure and temperature.

A growth process was performed as in Comparative Example 2. The NaHCO₃was in solid salt form on the substrate just prior to commencing thegrowth process. FIGS. 14A-F are SEM images showing carbon nanotubesproduced during the growth process.

Example 12

This example demonstrates carbon-based nanostructure growth from a NaOHactive growth material supported by a titanium substrate. Titaniumsheets (McMaster-Carr 9051K67 Grade 2) were sanded with 500 gritsandpaper, rinsed with deionized water, and dried under ambientconditions. A 0.18M NaOH in methanol solution was prepared and allowedto fully dissolve over the course of 1 hour. This NaOH solution was thendrop-cast onto titanium sheets and allowed to dry at room pressure andtemperature.

A growth process was performed as in Comparative Example 2. The NaOH wasin solid salt form on the substrate just prior to commencing the growthprocess. FIGS. 15A-F are SEM images showing carbon nanotubes producedduring the growth process. Carbon nanotube growth was also observed at400° C.

Example 13

This example shows carbon-based nanostructure growth from a NaOH activegrowth material supported by a titanium substrate. Titanium sheets(McMaster-Carr 9051K67 Grade 2) were sanded with 500 grit sandpaper,rinsed with deionized water, and dried under ambient conditions. A 0.18MNaOH in methanol solution was prepared and allowed to fully dissolveover the course of 1 hour. This NaOH solution was then spin coated ontothe titanium sheets and allowed to dry at room pressure and temperature.

A growth process was performed as in Comparative Example 2. The NaOH wasin solid salt form on the substrate just prior to commencing the growthprocess. FIGS. 16A-D are SEM images showing carbon nanotubes producedduring the growth process. Carbon nanotube growth was also observed at400° C.

Example 14

This example describes further demonstration of low-temperaturesynthesis of carbon nanostructures (CNS), such as CNTs, from commonhousehold Na-based compounds including NaHCO₃, Na₂CO₃, NaOH, and NaCl,found in baking soda, detergents, and table salt respectively. Coupledwith a temperature reducing oxidative dehydrogenation reaction to crackacetylene, Na metal nanoparticles catalyzed growth at temperatures below400° C. Ex situ and in situ transmission electron microscopy wereutilized to characterize the spatial composition of the CNS and Nacatalyst particles during growth. Unique CNS morphologies and growthphenomena were observed, including a vanishing catalyst phenomenon,i.e., CNTs without residual catalyst particles, that may be useful inapplications where metal catalysts are considered contaminants.

In this example, a variety of common household items have been found tobe effective in high-yield synthesis of CNT. Sodium-based compounds inparticular (such as table salt, baking soda, washing soda, and lye) haveallowed for the production of conformal coatings of CNT on carbonfibers. Aqueous catalyst solutions were prepared by dissolvingsemiconductor grade NaOH in water with the following concentrations:0.18M, 0.018M, and 0.0018M. NaOH solutions with the same concentrationswere also prepared in methanol. Likewise, aqueous solutions withequivalent concentrations were prepared for Na₂CO₃, NaHCO₃, and NaCl.These solutions were dipcoated or dropcasted onto substrates fiveminutes after solution formation. The substrates were allowed to dryunder ambient conditions and then subjected to a low temperature thermalchemical vapor deposition process in which hydrogen was flushed throughthe sample during temperature ramp to 480° C. Subsequently a 1 to 1ratio of CO₂ and C₂H₂ gas mixture was flowed through the tube, resultingin carbon deposition through an oxidative dehydrogenation reaction.Scanning electron micrographs (SEM) were taken of the fabrics for eachgrowth attempt, which showed conformal coating of carbon nanotubesaround each fiber as seen in FIG. 17. Transmission electron microscopywas also performed along with electron energy loss spectroscopy on thenanostructures to confirm carbon based tube morphology. To test forgrowth from contaminants, NaOH dipcoated fiber samples were subjected tothe initial reduction step inside the CVD furnace and stoppedimmediately before carbon gas introduction. These specimens were thenanalyzed under Energy Dispersive X-ray Spectroscopy (EDS) mapping inSEM, demonstrating that the catalyst particles formed contained largecounts of Na and O and no common transition metal catalysts (nickel,iron, and cobalt were not observed). Other substrates were alsosuccessfully used (while utilizing sodium for catalyzing CNT growth), asshown in FIG. 18. Fabric systems such as alumina fibers and unsized andpolymer-sized (coated) carbon fibers both yielded CNT growth. Sodium wasalso effective in promoting growth of CNT on flat substrates, includingbut not limited to silicon nitride TEM grids, silicon wafer chips, andtitanium sheets. For each of these processes, a 0.18 M NaOH in methanolsolution was drop-casted/spin coated to allow for an even deposition.TEM was performed for each sample to confirm the tubular morphology ofthe carbon nanostructure.

Growth temperatures were also varied from 390° C. to 820° C. whilekeeping all other treatments constant, such as the 15-minute growthduration. As shown in FIG. 19, CNTs were observed to be longer andexhibit more curled structures at higher temperatures. CNTs were alsoobserved to have other morphologies, such as open-ended morphologiesthat lacked catalyst particles and half-filled hollow morphologies.

In one set of experiments, the ratio of C₂H₂ to CO₂ was varied. As shownin FIG. 20, decreasing concentrations of C₂H₂ and increasingconcentrations of CO₂ resulted in the formation of CNTs with lowertortuosities.

Extensive TEM and energy dispersive X-ray spectroscopy (EDS) after 15minutes of CNT growth did not reveal clear particles attached to eitherthe base or tip of the tube (see FIG. 21). Scans across the full lengthof tubes also did not reveal contaminant particles such as iron ornickel. Additionally, no sodium particles were found directly attachedto the tube. Instead, scanning transmission electron microscopy revealeda somewhat brighter region on the inner wall of the CNT. Small area EDSscans of the lining compared with the adjacent outer wall revealed thata higher concentration of sodium existed on the interior of the tube,and showed that sodium residues lined the interior of the CNTs. In somecases, no sharp Na spike near the walls of the tubes was observed.

To better find the sodium catalyst particle for characterization throughex situ experimentation, CVD was performed on NaOH-dropcasted siliconnitride TEM grids for different growth durations. Specimens that hadonly been reduced with hydrogen (and had no exposure to CO₂ and C₂H₂)resulted in the formation of sodium-based nanoparticles. These particleswere observed to have strong electron beam interactions, oftendisappearing after several minutes of imaging. Meanwhile, exposing thespecimens to CO₂ and C₂H₂ for 15 minutes resulted in tubes with noparticles attached (FIG. 21). However, growths that were terminated atlow times at 1.9 and 3.8 minutes revealed the presence of clearparticles at the base of newly nucleated tubes. EDS scans on theseparticles revealed large concentrations of sodium. Additionally, theseparticles disappeared upon longer beam imaging. Some scalloping couldalso be found on the interior of the tubes.

In situ TEM was performed using an environmental transmission electronmicroscope (ETEM). During ETEM experiments, NaOH-dropcasted siliconnitride TEM grids were heated to 480° C. and flown with the followinggas feedstocks: 0.4 sccm H₂ during a 5 minute ramp from 25° C. to 480°C. followed by 0.1 sccm CO₂ and 0.1 sccm C₂H₂ at 480° C. for 30 minutes.Then, the sample was cooled to room temperature in the absence of anygas flow. Care was taken to achieve as close of a process match to thetube furnace as possible. Growth of carbon nanostructures wassuccessfully achieved while performing real-time imaging andcharacterization. Structures grown in the ETEM chamber were primarilysolid and contained a core-shell structure of carbon walls surrounding asodium carbonate interior. However, upon performing an electron energyloss spectroscopy (EELS) line scan across the structure, a clear coreshell structure was observed: high intensities of carbon walls weredetected on the outside of the structure, filled with a core with largecounts of sodium and carbonate oxygen and carbon. While solid, thesestructures are closely related to the hollow CNT found in ex situresults with sodium inner wall residues.

Further imaging of the solid carbon nanostructure formed inside the ETEMyielded a previously unobserved phenomenon, shown in FIG. 22. Thesodium-rich core of the nanostructure started to deplete from the tip ofthe tube and descended along the length of the tube towards the base.Subsequently, at longer beam exposures, the attached sodium particle atthe base of the tube also disappeared and rose up to reach the firstdepletion front to hollow out the structure, forming a CNT that wasvirtually identical to that observed in ex situ experiments. Inaddition, preliminary work has also shown that alkali metals withsimilar chemical reactivity such as potassium can catalyze growth of CNTin similar CVD environments.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,and/or methods, if such features, systems, articles, materials, and/ormethods are not mutually inconsistent, is included within the scope ofthe present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

1. A method of growing carbon-based nanostructures, comprising: exposinga precursor of the carbon-based nanostructures to an active growthmaterial comprising at least one of an alkali metal and an alkalineearth metal to grow the carbon-based nanostructures from the precursorof the carbon-based nanostructures, wherein: the active growth materialis at a temperature of less than or equal to 500° C. during the growthof the carbon-based nanostructures; and the active growth material doesnot contain iron or contains iron in an amount such that the ratio ofthe number of atoms of iron in the active growth material to thecombined number of atoms of any alkali metals and any alkaline earthmetals in the active growth material is less than or equal to 3.5.
 2. Amethod of growing carbon-based nanostructures, comprising: exposing aprecursor of the carbon-based nanostructures to an active growthmaterial comprising at least one of an alkali metal and an alkalineearth metal to grow the carbon-based nanostructures from the precursorof the carbon-based nanostructures, wherein the active growth materialis at a temperature of less than or equal to 475° C. during the growthof the carbon-based nanostructures.
 3. A method of growing carbon-basednanostructures, comprising exposing a precursor of the carbon-basednanostructures to an active growth material comprising at least one ofan alkali metal and an alkaline earth metal to grow the carbon-basednanostructures from the precursor of the carbon-based nanostructures. 4.(canceled)
 5. The method of claim 1, wherein the active growth materialcomprises an alkaline earth metal.
 6. The method of claim 1, wherein theactive growth material comprises an alkali metal.
 7. The method of claim1, wherein the active growth material comprises at least one of sodiumand potassium.
 8. The method of claim 1, wherein the active growthmaterial, or a precursor thereof, comprises at least one of a hydroxidesalt of an alkaline earth metal and a hydroxide salt of an alkali metal.9. The method of claim 1, wherein the active growth material, or aprecursor thereof, comprises at least one of a carbonate salt of analkaline earth metal and a carbonate salt of an alkali metal.
 10. Themethod of claim 1, wherein the active growth material, or a precursorthereof, comprises at least one of a bicarbonate salt of an alkalineearth metal and a bicarbonate salt of an alkali metal.
 11. The method ofclaim 1, wherein the alkali metal and/or the alkaline earth metal is acation of a salt.
 12. (canceled)
 13. The method of claim 1, wherein atleast 50% of the carbon-based nanostructures that are grown are indirect contact with the at least one of an alkali metal and an alkalineearth metal. 14-16. (canceled)
 17. The method of claim 1, wherein theactive growth material is supported on a polymeric substrate.
 18. Themethod of claim 1, wherein the active growth material is supported onone or more of a carbon fiber, a glass fiber, and an alumina fiber. 19.The method of claim 1, wherein the active growth material is supportedon a sized carbon fiber.
 20. The method of claim 1, wherein the activegrowth material is supported on at least one of a prepreg, a tow, and aweave.
 21. The method of claim 1, wherein the precursor of thecarbon-based nanostructures comprises acetylene.
 22. The method of claim1, wherein the precursor of the carbon-based nanostructures comprisescarbon dioxide.
 23. The method of claim 1, wherein the precursor of thecarbon based-nanostructures comprises at least one of a hydrocarbon andan alcohol. 24-26. (canceled)
 27. The method of claim 1, wherein thecarbon-based nanostructures comprise at least one of carbon nanotubes,carbon nanofibers, and carbon nanowires.
 28. The method of claim 1,wherein the active growth material is at a temperature of less than orequal to 500° C. during the growth of the carbon-based nanostructures.29-45. (canceled)